SpaceSniffer: Find Out What's Hogging Your Hard Drive

I found another good tool for Windows systems today while helping someone with a full hard drive problem. It's called SpaceSniffer and it presents you with a graphical layout of your Drive (or a particular folder) in boxes sized relative to the amount of space they occupy. There are controls to go deeper or shallower if you need extra detail on what is taking up the space. The site says you can also filter for particular file types and ages, but I haven't tried that yet.