SysInternals Utilities
http://technet.microsoft.com/en-us/sysinternals/default.aspx
If you learn all the tools, you can diagnose and troubleshoot some very complex system problems, crashes, annoyances, bugs, incompatibilities, CPU hogs, program lockups, etc.
There are a few utilities that are very useful by people who just want their computers to run well. (more…)