What's on your hard drive?

I have a 9.5 gig hard drive, of which over 7 gigs are currently filled. And I ask myself, "what's taking up all that space?" Thankfully, I've been introduced to some nice freeware that can help me solve that riddle.

I downloaded TreeSize 1.7, and it's helped a bit so far. FolderSize does much the same thing, and TreeMap 4.0 apparently is really neat, but it has to be started from a "DOS batch file," and I don't even know what that means.

All these links are courtesy of TechTV's ScreenSavers, whose page has a little more detail on each of these programs.