I use two freeware apps. on a regular basis - CCleaner and RegSeeker. CCleaner gets rid of the CRAP (Hence the name CCleaner) that accumulates on your hard drive and which isn't needed. As far as RegSeeker goes, I know that some very great people who post here, especially JohnWill (whom I respect very much and who's posts I really enjoy reading daily and religously), think that messing with the registry is very dangerous and unecessary, some of us are just anal and can't help ourselves.

I've been using it for a very long time, I only select the green items and I've never had any adverse effects. It also automatically makes a backup before cleaning. Advanced Windows Care is also a very good app. But you have to know what you're doing with that one with version 2. Anyways, just my thoughts.