Here is an updated version of my diagnostic information queries for SQL Server 2005. You can get the SQL Server 2008 version here. Most of the DMV queries require VIEW SERVER STATE permission.

-- SQL Server 2005 Diagnostic Information Queries
-- Glenn Berry 
-- November 2009
-- http://glennberrysqlperformance.spaces.live.com/
-- Twitter: GlennAlanBerry


-- SQL Version information for current instance
SELECT @@VERSION AS [SQL Version Info];

--   2005 SP2 Builds                  2008 SP3 Builds
-- Build       Description        Build       Description
-- 3042        SP2 RTM              4035        SP3 RTM
-- 3161        SP2 CU1              4207        SP3 CU1
-- 3175        SP2 CU2              4211        SP3 CU2 
-- 3186        SP2 CU3              4220        SP3 CU3         
-- 3200        SP2 CU4              4226        SP3 CU4         
-- 3215        SP2 CU5              4230        SP3 CU5          
-- 3228        SP2 CU6              4266        SP3 CU6        
-- 3239        SP2 CU7          
-- 3257        SP2 CU8
-- 3282        SP2 CU9
-- 3294        SP2 CU10
-- 3301        SP2 CU11
-- 3315        SP2 CU12
-- 3325        SP2 CU13
-- 3328        SP2 CU14
-- 3330        SP2 CU15
-- 3355        SP2 CU16
 
-- Hardware Information for SQL Server 2005
-- (Cannot distinguish between HT and multi-core)
SELECT cpu_count AS [Logical CPU Count], hyperthread_ratio AS [Hyperthread Ratio],
cpu_count/hyperthread_ratio AS [Physical CPU Count], 
physical_memory_in_bytes/1048576 AS [Physical Memory (MB)]
FROM sys.dm_os_sys_info;

-- get sp_configure values for instance
EXEC sp_configure 'Show Advanced Options', 1;
GO
RECONFIGURE;
GO
EXEC sp_configure;

-- Focus on
-- clr enabled (only enable if you need it)
-- lightweight pooling (should be zero)
-- max degree of parallelism
-- max server memory (MB)
-- priority boost (should be zero)


-- File Names and Paths for TempDB and all user databases in instance 
SELECT [dbid], fileid, [filename] 
FROM sys.sysaltfiles
WHERE [dbid] > 4 AND [dbid] <> 32767
OR [dbid] = 2;

-- Things to look at:
-- Are data files and log files on different drives?
-- Is everything on C: drive?
-- Is TempDB on dedicated drives?
-- Are there multiple data files?

-- Recovery model, log reuse wait description, and compatibility level for all databases on instance
SELECT [name], recovery_model_desc, log_reuse_wait_desc, [compatibility_level] 
FROM sys.databases;

-- Things to look at
-- How many databases are on the instance?
-- What recovery models are they using?
-- What is the log reuse wait description?
-- What compatibility level are they on?


-- Clear Wait Stats
-- DBCC SQLPERF('sys.dm_os_wait_stats', CLEAR);

-- Isolate top waits for server instance since last restart or statistics clear
WITH Waits AS
(SELECT wait_type, wait_time_ms / 1000. AS wait_time_s,
    100. * wait_time_ms / SUM(wait_time_ms) OVER() AS pct,
    ROW_NUMBER() OVER(ORDER BY wait_time_ms DESC) AS rn
 FROM sys.dm_os_wait_stats
 WHERE wait_type NOT IN( 'SLEEP_TASK', 'BROKER_TASK_STOP', 
  'SQLTRACE_BUFFER_FLUSH', 'CLR_AUTO_EVENT', 'CLR_MANUAL_EVENT',
  'LAZYWRITER_SLEEP')) -- filter out additional irrelevant waits
SELECT W1.wait_type, 
  CAST(W1.wait_time_s AS DECIMAL(12, 2)) AS wait_time_s,
  CAST(W1.pct AS DECIMAL(12, 2)) AS pct,
  CAST(SUM(W2.pct) AS DECIMAL(12, 2)) AS running_pct
FROM Waits AS W1
INNER JOIN Waits AS W2
ON W2.rn <= W1.rn
GROUP BY W1.rn, W1.wait_type, W1.wait_time_s, W1.pct
HAVING SUM(W2.pct) - W1.pct < 95; -- percentage threshold

-- Common Significant Wait types with BOL explanations

-- *** Network Related Waits ***
-- ASYNC_NETWORK_IO        Occurs on network writes when the task is blocked behind the network

-- *** Locking Waits ***
-- LCK_M_IX                Occurs when a task is waiting to acquire an Intent Exclusive (IX) lock
-- LCK_M_IU                Occurs when a task is waiting to acquire an Intent Update (IU) lock
-- LCK_M_S                Occurs when a task is waiting to acquire a Shared lock

-- *** I/O Related Waits ***
-- ASYNC_IO_COMPLETION  Occurs when a task is waiting for I/Os to finish
-- IO_COMPLETION        Occurs while waiting for I/O operations to complete. 
--                      This wait type generally represents non-data page I/Os. Data page I/O completion waits appear 
--                      as PAGEIOLATCH_* waits
-- PAGEIOLATCH_SH        Occurs when a task is waiting on a latch for a buffer that is in an I/O request. 
--                      The latch request is in Shared mode. Long waits may indicate problems with the disk subsystem.
-- PAGEIOLATCH_EX        Occurs when a task is waiting on a latch for a buffer that is in an I/O request. 
--                      The latch request is in Exclusive mode. Long waits may indicate problems with the disk subsystem.
-- WRITELOG             Occurs while waiting for a log flush to complete. 
--                      Common operations that cause log flushes are checkpoints and transaction commits.
-- PAGELATCH_EX            Occurs when a task is waiting on a latch for a buffer that is not in an I/O request. 
--                      The latch request is in Exclusive mode.
-- BACKUPIO                Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data

-- *** CPU Related Waits ***
-- SOS_SCHEDULER_YIELD  Occurs when a task voluntarily yields the scheduler for other tasks to execute. 
--                      During this wait the task is waiting for its quantum to be renewed.

-- THREADPOOL            Occurs when a task is waiting for a worker to run on. 
--                      This can indicate that the maximum worker setting is too low, or that batch executions are taking 
--                      unusually long, thus reducing the number of workers available to satisfy other batches.
-- CX_PACKET            Occurs when trying to synchronize the query processor exchange iterator 
--                        You may consider lowering the degree of parallelism if contention on this wait type becomes a problem


-- Signal Waits for instance
SELECT CAST(100.0 * SUM(signal_wait_time_ms) / SUM (wait_time_ms) AS NUMERIC(20,2)) AS [%signal (cpu) waits],
       CAST(100.0 * SUM(wait_time_ms - signal_wait_time_ms) / SUM (wait_time_ms) AS NUMERIC(20,2)) AS [%resource waits]
FROM sys.dm_os_wait_stats;

-- Signal Waits above 10-15% is usually a sign of CPU pressure


-- Get CPU Utilization History (SQL 2005 Only)
DECLARE @ts_now bigint; 
SELECT @ts_now = cpu_ticks / CONVERT(float, cpu_ticks_in_ms) FROM sys.dm_os_sys_info; 

SELECT TOP(30) SQLProcessUtilization AS [SQL Server Process CPU Utilization], 
               SystemIdle AS [System Idle Process], 
               100 - SystemIdle - SQLProcessUtilization AS [Other Process CPU Utilization], 
               DATEADD(ms, -1 * (@ts_now - [timestamp]), GETDATE()) AS [Event Time] 
FROM ( 
      SELECT record.value('(./Record/@id)[1]', 'int') AS record_id, 
            record.value('(./Record/SchedulerMonitorEvent/SystemHealth/SystemIdle)[1]', 'int') 
            AS [SystemIdle], 
            record.value('(./Record/SchedulerMonitorEvent/SystemHealth/ProcessUtilization)[1]', 
            'int') 
            AS [SQLProcessUtilization], [timestamp] 
      FROM ( 
            SELECT [timestamp], CONVERT(xml, record) AS [record] 
            FROM sys.dm_os_ring_buffers 
            WHERE ring_buffer_type = N'RING_BUFFER_SCHEDULER_MONITOR' 
            AND record LIKE '%<SystemHealth>%') AS x 
      ) AS y 
ORDER BY record_id DESC;


-- Page Life Expectancy (PLE) value for default instance
SELECT cntr_value AS [Page Life Expectancy]
FROM sys.dm_os_performance_counters
WHERE OBJECT_NAME = 'SQLServer:Buffer Manager' -- Modify this if you have named instances
AND counter_name = 'Page life expectancy';

-- PLE is a good measurement of memory pressure
-- Higher PLE is better. Below 300 is generally bad.
-- Watch the trend, not the absolute value


-- Buffer Pool Usage for instance
SELECT TOP(20) [type], SUM(single_pages_kb) AS [SPA Mem, Kb] 
FROM sys.dm_os_memory_clerks 
GROUP BY [type]  
ORDER BY SUM(single_pages_kb) DESC;

-- CACHESTORE_SQLCP  SQL Plans         - These are cached SQL statements or batches that aren't in 
--                                     stored procedures, functions and triggers
-- CACHESTORE_OBJCP  Object Plans      - These are compiled plans for stored procedures, 
--                                     functions and triggers
-- CACHESTORE_PHDR   Algebrizer Trees  - An algebrizer tree is the parsed SQL text that 
--                                     resolves the table and column names



-- Switch to user database *******************
--USE YourDatabaseName;
--GO

-- Individual File Sizes and space available for current database
SELECT name AS [File Name] , physical_name AS [Physical Name], size/128 AS [Total Size in MB],
size/128.0 - CAST(FILEPROPERTY(name, 'SpaceUsed') AS int)/128.0 AS [Available Space In MB]
FROM sys.database_files;

-- Look at how large and how full the files are and where they are located
-- Make sure the transaction log is not full!!


-- Cached SP's By Execution Count (SQL 2005)
SELECT TOP(25) qt.[text] AS [SP Name], qs.execution_count AS [Execution Count],  
qs.execution_count/DATEDIFF(Second, qs.creation_time, GETDATE()) AS [Calls/Second],
qs.total_worker_time/qs.execution_count AS [AvgWorkerTime],
qs.total_worker_time AS [TotalWorkerTime],
qs.total_elapsed_time/qs.execution_count AS [AvgElapsedTime],
qs.max_logical_reads, qs.max_logical_writes, qs.total_physical_reads, 
DATEDIFF(Minute, qs.creation_time, GetDate()) AS [Age in Cache]
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.[sql_handle]) AS qt
WHERE qt.[dbid] = DB_ID() -- Filter by current database
ORDER BY qs.execution_count DESC;


-- Cached SP's By Worker Time (SQL 2005) Worker time relates to CPU cost
SELECT TOP(25) qt.[text] AS [SP Name], qs.total_worker_time AS [TotalWorkerTime], 
qs.total_worker_time/qs.execution_count AS [AvgWorkerTime],
qs.execution_count AS [Execution Count], 
ISNULL(qs.execution_count/DATEDIFF(Second, qs.creation_time, GETDATE()), 0) AS [Calls/Second],
ISNULL(qs.total_elapsed_time/qs.execution_count, 0) AS [AvgElapsedTime], 
qs.max_logical_reads, qs.max_logical_writes, 
DATEDIFF(Minute, qs.creation_time, GETDATE()) AS [Age in Cache]
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.[sql_handle]) AS qt
WHERE qt.[dbid] = DB_ID() -- Filter by current database
ORDER BY qs.total_worker_time DESC;


-- Cached SP's By Logical Reads (SQL 2005) Logical reads relate to memory pressure
SELECT TOP(25) qt.[text] AS [SP Name], total_logical_reads, 
qs.execution_count AS [Execution Count], total_logical_reads/qs.execution_count AS [AvgLogicalReads],
qs.execution_count/DATEDIFF(Second, qs.creation_time, GETDATE()) AS [Calls/Second], 
qs.total_worker_time/qs.execution_count AS [AvgWorkerTime],
qs.total_worker_time AS [TotalWorkerTime],
qs.total_elapsed_time/qs.execution_count AS [AvgElapsedTime],
qs.total_logical_writes,
qs.max_logical_reads, qs.max_logical_writes, qs.total_physical_reads, 
DATEDIFF(Minute, qs.creation_time, GETDATE()) AS [Age in Cache]
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.[sql_handle]) AS qt
WHERE qt.[dbid] = DB_ID() -- Filter by current database
ORDER BY total_logical_reads DESC;


-- Possible Bad Indexes (writes > reads)
SELECT OBJECT_NAME(s.[object_id]) AS [Table Name], i.name AS [Index Name], i.index_id,
        user_updates AS [Total Writes], user_seeks + user_scans + user_lookups AS [Total Reads],
        user_updates - (user_seeks + user_scans + user_lookups) AS [Difference]
FROM sys.dm_db_index_usage_stats AS s WITH (NOLOCK)
INNER JOIN sys.indexes AS i WITH (NOLOCK)
ON s.[object_id] = i.[object_id]
AND i.index_id = s.index_id
WHERE OBJECTPROPERTY(s.[object_id],'IsUserTable') = 1
AND s.database_id = DB_ID()
AND user_updates > (user_seeks + user_scans + user_lookups)
AND i.index_id > 1
ORDER BY [Difference] DESC, [Total Writes] DESC, [Total Reads] ASC;


-- Missing Indexes for entire instance by Index Advantage
SELECT user_seeks * avg_total_user_cost * (avg_user_impact * 0.01) AS [index_advantage], migs.last_user_seek, 
mid.[statement] AS [Database.Schema.Table],
mid.equality_columns, mid.inequality_columns, mid.included_columns,
migs.unique_compiles, migs.user_seeks, migs.avg_total_user_cost, migs.avg_user_impact
FROM sys.dm_db_missing_index_group_stats AS migs WITH (NOLOCK)
INNER JOIN sys.dm_db_missing_index_groups AS mig WITH (NOLOCK)
ON migs.group_handle = mig.index_group_handle
INNER JOIN sys.dm_db_missing_index_details AS mid WITH (NOLOCK)
ON mig.index_handle = mid.index_handle
ORDER BY index_advantage DESC;

-- Look at last user seek time, number of user seeks to help determine source and importance
-- SQL Server is overly eager to add included columns, so beware


-- Breaks down buffers used by current database by object (table, index) in the buffer cache
SELECT OBJECT_NAME(p.[object_id]) AS [ObjectName], p.[object_id], 
p.index_id, COUNT(*)/128 AS [buffer size(MB)],  COUNT(*) AS [buffer_count] 
FROM sys.allocation_units AS a
INNER JOIN sys.dm_os_buffer_descriptors AS b
ON a.allocation_unit_id = b.allocation_unit_id
INNER JOIN sys.partitions AS p
ON a.container_id = p.hobt_id
WHERE b.database_id = DB_ID()
AND p.[object_id] > 100
GROUP BY p.[object_id], p.index_id
ORDER BY buffer_count DESC;

-- Tells you what tables and indexes are using the most memory in the buffer cache


-- Detect blocking (run multiple times)
SELECT t1.resource_type AS [lock type],DB_NAME(resource_database_id) AS [database],
t1.resource_associated_entity_id AS [blk object],t1.request_mode AS [lock req],                                                                          --- lock requested
t1.request_session_id AS [waiter sid], t2.wait_duration_ms AS [wait time], -- spid of waiter  
(SELECT [text] FROM sys.dm_exec_requests AS r                              -- get sql for waiter
CROSS APPLY sys.dm_exec_sql_text(r.[sql_handle]) 
WHERE r.session_id = t1.request_session_id) AS [waiter_batch],
(SELECT SUBSTRING(qt.[text],r.statement_start_offset/2, 
    (CASE WHEN r.statement_end_offset = -1 
    THEN LEN(CONVERT(nvarchar(max), qt.[text])) * 2 
    ELSE r.statement_end_offset END - r.statement_start_offset)/2) 
FROM sys.dm_exec_requests AS r
CROSS APPLY sys.dm_exec_sql_text(r.[sql_handle]) AS qt
WHERE r.session_id = t1.request_session_id) AS [waiter_stmt],    -- statement blocked
t2.blocking_session_id AS [blocker sid],                         -- spid of blocker
(SELECT [text] FROM sys.sysprocesses AS p                        -- get sql for blocker
CROSS APPLY sys.dm_exec_sql_text(p.[sql_handle]) 
WHERE p.spid = t2.blocking_session_id) AS [blocker_stmt]
FROM sys.dm_tran_locks AS t1 
INNER JOIN sys.dm_os_waiting_tasks AS t2
ON t1.lock_owner_address = t2.resource_address;