Must have Windows Utility -- Process Explorer

Since I work in the OS division, I image my work machines quite often. (Not as often as a lot of our test team, but more than most people.)

Besides putting my task bar at the top of the Window and switching my keyboard to Dvorak, there are also a set of utilities I download and install. Process Explorer is always at the top of the list. Think of it like Task Manager on steroids. You can see the process hierarchy, processor and memory usage per process (with graphs), and the set of handles and libraries in use by each process. My favorite feature is the ability to search for a file and see processes with handles to it. This is essential when you want to delete a file, but some unknown process is holding on to it.

Check it out.