From Eriban Software:
GrandPerspective is a small utility application for Mac OS X that graphically shows the disk usage within a file system. It can help you to manage your disk, as you can easily spot which files and folders take up the most space. It uses a so called tree map for visualisation. Each file is shown as a rectangle with an area proportional to the file's size. Files in the same folder appear together, but their placement is otherwise arbitrary.
What's new in this version:
It fixes two memory leaks (a large and a small one) and attempts to solve the crashes that some users have reported. It may fix the problem, but if not it will help in tracking the cause, as it generates additional logging to Console.