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 features two minor improvements both requested by users. Firstly, the ability to report file sizes with a decimal base. Secondly, the ability to copy the path of a selected item to the paste board. Also included is a minor bug fix.