CCleaner the Crap Cleaner

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! :)
CCleaner.com

This freeware (donationware actually). Is the best tools to clean up your PC from unused files such as internet history, internet browser cache from Internet Explorer, Mozilla Firefox and Opera, unused registry entries, and alot of unused application history in order to protect your privacy (if you were using a shared computer).