Registry Mechanic
I install literally hundreds of programs on my system every year. While I'm far from normal in that regard, it only takes one poorly designed uninstall or dodgy driver to cause problems in the Windows registry. Problems in the registry quickly escalate to problems with Windows stability. Enter Registry Mechanic, which quickly detects and repairs invalid or missing references in the registry. Configuring the application is push-button simple; check the boxes next to parts of your system that require scanning and start the scan. Registry Mechanic will detect and eliminate orphaned registry entries, remove bunk information from Add/Remove Programs, and generally optimize your system by clearing out unused information. A backup feature stores everything removed by the application, giving you time to verify nothing important was eliminated. As an example of just how effective Registry Mechanic really is, I started having strange blue screens almost daily following the uninstall of a cell phone application. On the verge of wiping my hard drive, I ran Registry Mechanic and the blue screen problem went away.