http://www.metronomeonline.com/- Online metronome! Bookmark this--you'll use it A LOT!
http://www.essentialsofmusic.com/- "The Essentials of Music" has information on musical eras, composers, and a great musical dictionary. Great for Music History and Vocab!
http://lab.andre-michelle.com/tonematrix- "The Tone Matrix" is a grid that creates different tones. Great for experimental composition!
http://www.stanwilliamsmusic.com/drums.html- Play virtual drums online
http://www.oddmusic.com/- "Odd Music" is where you will find world music, unusual compositions, and experimental music. Great for Listening Exercises!
http://musicovery.com/index.php?ct=us- Looking for just the right piece of music to match your mood? Then use this generator to pick your mood and style of music. You'll have a new favorite in no time!
http://www.virtualpiano.net- Play the piano online!
http://www.lullatone.com/blog/wp-content/uploads/2009/04/raindrop.swf- Play with another music generator shaped like raindrops. Great for working on timing!
http://oyc.yale.edu/music/listening-to-music- a course from Yale University about how to listen to music!!
http://www.eecs.harvard.edu/~nesson/sequencer.html- Help these sheep get their groove on!!