Music Tech Teacher - This page has a big list of quizzes and games that test your knowledge of music terms, rhythm, notes, instruments, composers, and more! Appropriate for upper elementary students.
NY Philharmonic KidZone - Lots of fun interactive activities from the New York Philharmonic Orchestra. Meet the musicians, learn about composers, build your own instruments, compose your own music, and more!
PBS Kids Music Games - Fun music games for elementary students of all ages!