I am a huge fan of tools that allow me to keep my OS clean, deal with my browser cache and prevent temp files from overwhelming my Hard Disk.
Pretty much every activity you perform on your PC leads to something being saved there; browsing, productivity and so on. It’s not always easy to track where all this stuff is being saved by the applications and system. These tools identify the locations and allow you to select what and where you get to clean up.
Three that I favor are Windows Washer, NCleaner and CCleaner. The first is an excellent tool, robust and stable with several updates per year but should be purchased. The other two are free and each does things slightly differently.
All have functionality that can affect the registry and contents of your hard drive so read carefully and backup files and registry (NCleaner and CCleaner have reg backup built in) prior to running a clean.
I would say that NCleaner has the broadest suite of options but with this perhaps the most potential for complications. The Tweak system option is for super-users who know what they are getting themselves into when they make these changes and the Real-time monitor keeps an eye on your CPU and Memory load/ stress.
I am somewhat circumspect as to their abilities to maintain a cleaner registry for me but that all depends how much Freeware/ Trialware/ Shareware you test as to how much your registry is affected. If you are a heavy software test user and want to keep the OS clean then think of either using VMWare as a test environment or Symantec Ghost to rollback to a clean OS and registry.