Scott Hanselman discovered another pretty good tool, CrapCleaner Registry, and it is FREE!
CCleaner is a freeware system optimization and privacy tool. It removes unused files from your system - allowing Windows to run faster and freeing up valuable hard disk space. It also cleans traces of your online activities such as your Internet history. But the best part is that it's fast (normally taking less that a second to run) and contains NO Spyware or Adware! :)
CrapCleaner from ccleaner.com
File Hippo - Free Software Download - I found it also contains a lot of free program, from all kinds of area.