Nothing fancy, just a simple program that clears the windows cache, stores files etc etc.
Its called:
CCleaner (Former name: Crap Cleaner).
Download it from here:
CCleaner - Download
After installation, simply open up the tool and hit "Run Cleaner". When done, it will display how many MB it has "cleaned" and removed.
When the first part is done, go click on "Registry" and choose "Scan for issues". This will search for .dll-files etc. that are no longer being used, and only takes up space.
When the scan is complete, choose "Fix selected issues" - you can now choose to backup your registry database (so far i havent discovered any problems at all by not doing so). Choose "Fix all selected issues".
Thats it. Helps a bit on startup and loading times.