Sometimes, I wonder where my gigabytes and gigabytes of storage have disappeared. In those cases, I often go back to Google (or Bing!) and search for SpaceMonger version 1.4. This utility is amazing. Not only is it free, but it really gives a great visual representation of disk allocation. You can see where disk space is disappearing.
Essentially, SpaceMonger is a bit like a million dollar homepage. The bigger the file or folder, the more space it takes in the view. So you can visually see where you disk space is going. Sometimes, it’s an eye opener: folders that you never realize existed contain huge file. In my case, this happened once recently. I had been using Windows Movie Maker to create a DVD, and didn’t realize it was creating temporary video files from my MPEG-2 sources. SpaceMonger found those for me, and I reclaimed over a gig of disk space.
Anyways, sometimes the best utilities are often the least flashy or least humongous. (Xtree Gold anyone?)