Piriform ccleaner is good as the others have said, it also comes with other nifty features, such as the ability to securely delete files from your computer using a 7 pass algorithm. It even lets you do that for all the free space of your drive, sodeleted files can't be recovered, should you have a need to hide the **** from a girlfriend or something, haha.
Edited, Jun 6th 2011 2:10pm by xthunderblazex