Useful Mac App: Disk Inventory X (Free)

Building on the ever-popular heat maps being used absolutely everywhere, it was only natural a visual disk usage utility would make its way to OS X. Load it up, point it to a directory or disk and let it run. When it is complete, it will load up a graphical map of your disk usage – with interactive click functions between the File Type page, the Finder-style directory listing, or the map.

Directory X