I like Performance Monitor (perfmon); its a good tool for diagnosing many different types of problems. Its great for determining from how well your memory is handling requests to how well your CPU usage is doing...its also great for checking out different SQL Server metrics. In SQL Server 2005, the sys.dm_os_performance_counters Dynamic Management View (DMV) is introduced to allow you to query SQL Server related performance counters directly through the database engine. This makes is very useful...