CCleaner
CCleaner is logically designed and makes it easy to remove unused files from your system, allowing Windows to run faster while freeing up valuable hard disk space. It also cleans traces of your online activity such as your internet history. But the best part is that it's fast, normally taking less than a second to run.
CCleaner also includes a safe and sound registry cleaner, an excellent startup manager, and a great program uninstaller.
If you'd like further information as to cleaning your system, visit this page on SafeHex or this one on Cleaning XP.
