“WinDirStat is a open source disk usage statistics viewer and cleanup tool for Microsoft Windows”:http://windirstat.sourceforge.net/.

It scans your disk and then shows you what folders and files are taking up the most space on your hard disk, producing both an expandable list of the directories on your hard disk, sorted by size, and a visualization, color-coded according to file type.

It takes a few minutes to gather all the information, but once its done, you can see at a glance what’s using the most space on your hard disk.