Disk usage analysis and cleanup tools

Disk usage analysis and cleanup tools: "Most of us use our hard disks like closets, stuffing in files and then forgetting about them. But no matter how big a disk you have, it's going to run out of free space one day, and running out of disk space during an OpenOffice.org install or a system update could hurt you badly. Keeping an eye on disk usage doesn't take much time or effort. Here are some tips and tools."