Have you ever wondered where all your free space on your hard drive has gone? Have you every wondered how to find files or folders that are taking up a lot of space? Or maybe what percent of your disk is taken up by the Windows directory?
Well if you have, I suggest using WinDirStat. It is OpenSource and thus free. It takes just a minute to download and install and takes around 1MB of diskspace. It is quite fast at analyzing your disk also. I highly recommend it.
Here is the link for info (including screenshots) and download links.