Every once in a while, I get low on disk space, and hunting for large directories or files to delete can be difficult manually. [Tree Map visualization](http://en.wikipedia.org/wiki/Treemap) tools make the job easier. There’s [WinDirStat](http://windirstat.info/) for Windows, [KDirStat](http://kdirstat.sourceforge.net) for KDE, and [Disk Usage Analyzer](http://live.gnome.org/GnomeUtils/Baobab) (baobab) for Gnome.
