SpaceMonger examines your hard drive to see where you’re using space, and displays this analysis to you in the form of rectangles — the bigger the rectangle, the more space that directory is taking up. You can drill down into the drive structure by clicking on rectangles. This may not seem like much, but I promise you that you’ll find a number of overlooked spacemongering files with this tool.
Last week, I couldn’t figure out why I only had 5GB free on a 60GB drive. SpaceMonger helped me find a long-forgotten directory full of 30GB worth of MySQL backups and an abandoned Crystal Decisions trial installation.