Music Theory and History Sites
This is a great site with training in music theory. It has lessons on various topics and trainers to help you learn notes on the staff, fingerings for brass instruments, how to spell chords, and a lot of other stuff.
AP Music Theory Links (in pdf format)
A video introduction to Music Appreciation
Elements of Music (World Music)
Music Theory On Line (Distance Learning Theory Course)
Music Theory Online (Online Music Theory Journal)
Dolmetsch Online - music site with various information including music theory
Center for Educator Development in Fine Arts (CEDFA) Links