Filelight allows you to take a look at your file usage by showing it in concentric circles and displaying it with upper parent directories as the inner rings and the files at the ends of the trees at the outer edge of the rings. This works for anything that runs QT and KDE. That means linux, folks.
Pretty neat stuff. Not something I’d use on a daily basis, but if you’re more graphically oriented, it’s definitely worth it. Me? Give me a commandline any day.