Grand Perspective
Originally uploaded by Rija 2.0.
Years (2 or 3?) ago, I was always struggling for space on my hard drive.
Although today I haven't go this problem on my desktop anymore. It still an issue on the laptops. One of the tool that I found helpful at that time, was a shareware from the Omni group, called omnidisksweeper.
It calculates the space taken by files and directories and then sort the results in the familiar NeXT-ish hierarchical multi-columns view that so pervasive in Mac OS X. If you've your shareware you can sweep entire files and directories at the push of a button. The premise being that the system and third party software create lots of temporary huge files that are not easily visible unless you know what you're looking for.
Grand Perspective is a software that goes further in helping you figure out where your disk space is going by constructing a two-dimensional map of the content of your hard-drive. Not only it gives you an at a glance view of the entire data usage but it's also not ugly to see :-)
And it's free and open source.