Music Theory
Music theory.net: Keyboard Trainer
A fantastic resource for music teachers and students learning to play the piano. This online quiz can be customized to test students on specific keys. Students can click "Toggle helpers," to check answers along the way.
Other
Piano Music Sight Reading Practice
Actually this clever site drills pianists on note names and note placement on the keyboard. Kids can access this site at home for practice. Both treble and bass clef are used.