+1 for Ccleaner. Considered one of the safer, gentler cleaners, for whiter whites without bleaching colours.
TweakNow
http://www.tweaknow.com/RegCleaner.html is another gentle tool.
Opinion varies as to what benefit is gained from reg cleaning. Unfortunately there are plenty of programs that, when uninstalled, leave orphans behind, and not just in the registry.
Also recommend
http://www.revouninstaller.com/ for this sort of thing. It will "deep search" for files/reg entries left over by a programs' own uninstaller.
Why the emphasis on "gentle"?
Also highly recommend backing up the registry before making changes.
It's possible to bork your OS by overzealous reg cleaning. (Been there, done that!) Ccleaner has the option to backup changes made, a good feature. I've also found Erunt
http://www.larshederer.homepage.t-online.de/erunt/ very good for this. The "NTREGOPT" program on the same page defrags the registry, without removing entries. Never had a problem. Some folk use Erunt in lieu of system restore.