Shortly after Leopard shipped, I found that I kept filling up my Time Machine drive. While some things I knew I had to exclude from Time Machine (like a giant database file), others weren't quite so obvious.
So I dug around on the Internet, and found the GrandPerspective project. What that lets you do is see graphically what files are taking up what space on your hard disk.
So far so good, except with Time Machine, large files that don't change don't matter. What matters are large files with constant small changes. Like database files, other mysterious stuff.
So I added a hack to GrandPerspective such that if a file was hard linked, which meant Time Machine was using it more then once, it get's reported as having a zero size. What that means is that you can scan a Time Machine backup folder, and look for those files that are filling up your Time Machine backup. Then you can exclude them, or go into Time Machine and remove them from your backup to claim space. There's a Tidbits article here with some suggestions on using it. Tidbits.
Anyways, you can download it from the link on your right. You'll want to run it over and over again to catch stuff that shows up in Time Machine you don't want.