http://www.jgoodies.com/freeware/jdiskreport/

Actually it's cross platform (java) and free, as an enticement for the parent company to check out their proprietory java gui sdk libaries.

Anyway, it's a good tool to help with disk space management on any OS. I know OmniDisksweeper is out there too as far a list views and detail, but JDiskReport has the pretty pie or bar graphs.