FindSpace is a simple application to display usage on your computer's disk in a tree form so you can root out any cruft left over from previous installs and generally find out where all that disk space is going.
To use, make sure to dissconnect any network drives and press the "Scan Now" button. Only the largest folders and files are shown sorted by size. Click on the folder icons to drill down to subfolders or the Folder name to view in Finder.