If you’ve ever felt frustrated reading the manual that comes with your Nikon D80 camera, a good alternative would be to download Ken Rockwell’s Nikon D80 User Guide.
Thom Hogan is another noted Nikon expert, and writes in a clear, succinct style which educates the interested photographer with a great deal of technical (and practical) notes and how-to’s.
His Complete Guide to the Nikon D80 is not free, but is worth every penny.