I use a program called TreeSize Pro at work to show me how a directory is being used.  It’s really useful when I ask a user to clean up their home drive and they come back and say, “I need everything that’s in there and it’s all work related!”.  After using the program and showing them that 90% of the space is taken up by MP3 and MPEG files, they generally change their tune (no pun intended).

I found a program for my Mac that’s even better.  Disk Inventory X inventories your hard drive and shows you a map that shows you relative file sizes and sort of groups them based on the type and location of the files.  Using it’s map, I was able to clean up about 15GB of unneeded data in about 5 minutes (damn GarageBand loops!).