Windirstat is colorful and nifty tool to check the makeup of your hard drive--especially if you're looking for immense files.
It scans your drive and produces a treemap that shows each file as a colored rectangle that's proportional to the file's size. For instance, in the attached screen capture, the big purplish blue rectangle on the left represents what seems like two billion MP3s; the green blob signifies images. Click on a filename in the left panel and it shows you where it is on the color grid below. Select a big block on the color grid and it leads you to the file. The toolbar includes buttons to zoom in on a color cluster, copy a path, open the file (or Windows Explorer), and, of course, delete files.