I am a big fan of the Sysinternals utilities, these are some of the best free utilities available for Windows. In fact, I liked these utilities so much that I have published a few articles on these programs in the past, such as: Process Explorer and AutoRuns.
Microsoft recent acquired Sysinternals, and hired its creators Mark Russinovich and Bryce Cogswell in July, 2006. Now they have publish the Sysinternals tools on their web site. In fact the old Sysinternals web site now redirects people to the Microsoft version of the site.
Since joining Microsoft, a new generation Process Explorer has been released called 'Process Monitor' which in fact combines a few utilities into one package.