[Note: edited to reflect updated name]
A little pet project of mine, DiskSlicer, has finally reached the 1.0 stage. It does one thing, but does it well: shows you your disk space is allocated among all the folders and files on your drives. It can be an invaluable tool for figuring out where all your space is going. Free for personal use!
Check out my latest book, the essential, in-depth guide to performance for all .NET developers:
Writing High-Performance.NET Code, 2nd Edition by Ben Watson. Available for pre-order: