Just found an open-source utility that maps out disk usage: WinDirStat <http://windirstat.info>
You let it run and it shows an overview of all of your disk usage. It also lets you delete selected files — nice!
The largest rectangles in the drive map are the largest files, click on one and it shows you its info and lets you manipulate it.
I have been working with laser scan point clouds recently. We fill up disk space very quickly; I think this will come in handy.