What's Taking Up All the Space On My Hard Drive?

If you're wondering that, I've discovered a type of tool, called a tree
map, that is thrillingly perfect for visualizing the hierarchical
structure of your hard drive and how much space different files and
folders take up. There are wonderful free implementations for the PC:

http://windirstat.info/

and Mac OS X:

http://grandperspectiv.sourceforge.net/

Try it!