1) 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. CCleaner also fixes your registry. But the best part is that it’s fast (normally taking less than a second to run) and contains NO Spyware or Adware.
http://www.ccleaner.com/

2) Advanced WindowsCare Personal is a comprehensive PC care utility that takes a one-click approach to help protect, repair, and optimize your computer.
http://www.iobit.com/

3) Eusing Free Registry Cleaner is a free registry repair software that allows you to safely clean and repair registry problems.
http://www.eusing.com/free_registry_cleaner/registry_cleaner.htm

4) Registry Distiller is a free registry cleaner that will optimize your system by removing obsolete and incorrect information from the registry, resulting in a faster computer that is less prone to errors.
http://www.codeode.com/registrydistiller/

5) TweakNow RegCleaner Standard is a free registry cleaner that will scour your system’s registry for useless/unneeded registry entries and optionally remove these for you. These entries are often left behind after the removal of software, cluttering the registry and possibly hindering your system’s overall performance.
http://www.tweaknow.com/RegCleaner.html