TreeSize Pro (http://www.jam-software.com/treesize/index.shtml) is a great tool that I've used for that purpose.
du -h --max-depth=3
A free one that I use is called SpaceMonger (http://www.werkema.com/software/spacemonger.html). Uses the nifty treemaps developed by HCI experts at University of Maryland's Human-Computer Interaction Laboratory by Dr. Ben Schneiderman.
SequoiaView ( http://www.win.tue.nl/sequoiaview/ )
Thank you, all you shiny happy people.
Try Diskdata - I've found it very useful. It is shareware and can be found at http://www.digallery.com/diskdata
"Folder Size Shell Extension" (you should search for it as such, in quotes)
DriveScan one of the components by Stardock
Another vote for SequoiaView. Like the man said, small and free. Just remember not to delete that huge pagefile.sys. :-)
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