For those out there interested in those commercials claiming to double your computer speed. Here are a few apps that help me clean my computers...
Visdir presents a pie chart (or optionally, a bar chart) where each slice is a subdirectory on your computer. Clicking a slice in the pie chart brings up a pie chart of that subdirectory, allowing you to recurse.
CCleaner is a freeware system optimization, privacy and cleaning tool. It removes unused files from your system - allowing Windows to run faster and freeing up valuable hard disk space.