TreeSize Free is a great tool that shows you all the files and folders on your hard drive and the size of them. It's great to use when you're running out of hard drive space and you want to delete something but don't know what.
Several years ago I ran this tool, and discovered a 2GB page file that wasn't used for several years. I deleted it and recovered 2GB so I didn't need to buy a new hard drive right away. TreeSize Free is freeware.