The Sysinternals tools have been popular for years and years - they do what they do exceedingly well, and can help troubleshoot all sorts of problems. Well, using them just got easier - as this post announces, there is a beta Sysinternals Live service that allows you to run them from a command line or the Start | Run menu simply by typing \\live.sysinternals.com\tools\<tool-name>.
The list of tools is at http://live.sysinternals.com/, and you can find a general readme file at http://live.sysinternals.com/About_This_Site.txt. And finally, if you're not sure what each tools does (there's a bunch of them!), you can find a reference here.