CrapCleaner Registry Cleaner
Wow, a tool I hadn't heard of. I've used RegClean and RegMaid and the like, but I'm totally impressed with (specifically) the Registry cleaning abilities of the Crap Cleaner. Recommended. (Use at your own risk. That means you, cousin Jack and my Dad. I'll run it on your system next time I'm over there.)
This is definitely on my list of "Things To Run When Visiting Relatives During The Holidays And They Ask You To Take A Look At Their Computer."
AdAware, SpyBot, Windows Disk Cleanup (with Shawn Van Ness' cleanup addons) and now Crap Cleaner.