Notation

Practical Music Theory
Work your way through the several online books to help teach others about music theory. Read the articles section that carries content ranging from Villa-Lobos to Thirteenth Century Polyphony. An extensive quiz section to test your knowledge of music theory and music exercises that you can practice online if you have a Java-capable browser.

The Random Music for Y2K Project
If you are tired of the standard music theory sites, try looking up this truly fascinating page that offers you an opportunity to compose music onsite. You can also download different programs to create music, or you can choose to just listen to the MIDI collection. It's great fun for lovers of modern music.