My youngest was (and is) highly musical. You've already had some grea suggestions about exposure to a wide variety of music styles, purchasing a sturdy keyboard, and I'd recommend whatever version of leap pad is now available. They have some wonderful musical software geared for children that is interactive and tactile. Resist the urge to take control of the experiences to make them more educational - what worked well for my kiddo was to be accessible if he couldn't make something work correctly but to let him just explore and experience. He would spend hours at the keyboard or playing with the leap pad music books, and he still plays his keyboard most days before heading to school.
