I prefer Treesize Pro.
I heartily second this recommendation. You get to see the folders’ names and their size in proportion to the rest of the disk, subfolders included. Highlight them and see the size in MB or GB. Incredibly simple and useful tool for clearing out space.
The WinDirStat download seems to be working again.
Since I’m sure ya’ll are worried sick, I wanted to update: I had no joy from the website (actually links to sourceforge I think), but got a working copy from PCWorld or somewhere, by googling windirstat.
Once, from 196.019.60.196, for 20 megabytes.
Turn off the hibernate function if it’s on. It can take up much space that is needed by you.
You’ll find a wide variety of Windows treatments and solutions at this web site.
You. Bastard.
Now those poor people are going to be wondering why they got so much traffic today.
Not a problem. Somebody might buy something. I use one of their systems, and I’m very happy with it. 
HA!
Treesize is a utility that shows you the contents of a directory tree by size- if you click on c:, you’ll see a pie-chart of all the root-level directories of C: by size.
Double-click on the largest, and you’ll see the same kind of thing, only one level deeper.
It’s a really fast and easy way to find out where the really big stuff is being stored.
I use this one also. Works really fast on mapped drives to Netware servers as well.
WinDirStat is magnificent, I’ve been showing it off to cow-orkers and family (some of which are one and the same.) All your files in their glorious squarity there for you to look at and quickly see which are the biggiest.
Well, if WinDirStat doesn’t do it for you , you might try blasting your hard drive with a 1920’s style death ray. I’ve heard that frees up a lot of space.
Ah, but that doesn’t make it taste like bacon, now does it? If only there was a way to make it taste like bacon…