Music Theory

Music Theory From the Beginning
Music Theory & Ear Training
Finale Music (free download)  

Sites for Kids to Explore

 Play the Xylophone  (Takes a while to load, but worth it)
Freaky Frank's Music Machine
Thumb Piano
Juice Bottle Jingles
Creating Music
SanFrancisco Symphony for Kids
Dallas Symphany for Kids

Resources

Virtual Keyboard
Great Composers
Sing Along Songs
The Enjoyment of Music (Online Tutor)
Music Flash Cards
More Flashcards 
Music Rack
Music Links
Music Education Madness(ppts & other resources)
Music Guides, Reviews, & Resources
Clapping Rhythms