Free Administrative Tools

In my quest to track down and stop all unneeded services running in my Windows Task Manager I came across a collection of programs to aid me in this process. Besides being a great set of tools they are freeware.
Sysinternals has an impressive collection of free tools, including Process Explorer, that tells you more than you probably thought was possible about programs running in your system, Filemon, which shows you all activity in your file system in real time, Regmon, which lets you see all registry activity in real-time, and TCPView, which shows you the names of programs on your system that are communicating over TCP/IP or UDP. Many of these tools are available in source code form.