CCleaner (formerly Crap Cleaner) is a freeware system optimization and privacy tool. It removes unused and temporary files from your system - allowing Windows to run faster, more efficiently and giving you more hard disk space. The best part is that it's fast! (normally taking less than a second to run) and Free.

Cleans the following:

• Internet Explorer Cache, History, Cookies, Index.dat.
• Recycle Bin, Temporary files and Log files.
• Recently opened URLs and files.
• Third-party application temp files and recent file lists (MRUs).
  Including: Firefox, Opera, Media Player, eMule, Kazaa, Google Toolbar, Netscape, Office XP, Nero, Adobe Acrobat, WinRAR, WinAce, WinZip and more...
• Advanced Registry scanner and cleaner to remove unused and old entries.
  Including File Extensions, ActiveX Controls, ClassIDs, ProgIDs, Uninstallers, Shared DLLs, Fonts, Help Files, Application Paths, Icons, Invalid Shortcuts and more... Backup for registry clean.
• Windows Startup tool.

If you like and use this software then it is polite to make a donation to the author.