I was hipped to this program by Lifehacker blog. WinDirStat is a program that analysis your hard drive(s) and shows it as a bunch of blocks, bigger files are bigger blocks allowing you to see whats taking up so much space. I know allot of people would be tempted to go on a delete-athon but try to resist as you could delete important files. But never the less an awesome program which is based on Stefan Hundhammer's KDE program KDirStat , and Re-programmed for Windows by BerdhardSeifert.
Get it here.