WinDirStat identifies how much disk space you're using and what it's being used for. Based on the Linux application KDirStat, and also available in a portable version, this great piece of freeware offers you an informative visual display of your hard-drive usage. It can also analyze local devices. Depending on the size of your disk, the initial WinDirStat scan may take quite a while, so be prepared to go grab a cup of coffee for 5 to 10 minutes.
When you return, you'll see all of your files for the selected drive or directory displayed in a rainbow of colors. WinDirStat assigns colors to each file type, such as MP3, ZIP, EXE, JPG, and so on. By default, the files that take up the most space are colored blue, the second heftiest are red, and the third largest green. After the first 10 color-labeled file types, the rest appear in gray--but you can change these settings and colors through the Options menu.
WinDirStat is loaded with features for file management, such as the ability to permanently delete files. It's one of those tools that you didn't know you needed until you started using it, but it's hard to imagine life without it once you've got it.