GrandPerspective identifies the files that eat up your disk space.
GrandPerspective, a Mac OS X utility program that graphically displays disk usage within a filesystem, is available for download. You can see which files and folders are taking up the most space, which can help you manage your disk. It uses a treemap to visualize. Each file is represented as a rectangle with an area proportional the file's dimensions. Although files in the same folder appear together at first glance, their placement is arbitrary.