I would suggest trying some orchestral music. I personally enjoy listening to orchestral works from the Classical or Baroque periods. Bach's organ music is also excellent to listen to (if done right), but the sharp sounds of the organ can be counter-productive to studying.
Something I also discovered that is great to listen to is soundtracks from movies. Movies such as Lord of the Rings, Narnia, and even music from the Star Trek movies and shows have some great non-lyrical music.
Also look at games for music. I have a space-sim (I am really putting myself out there as a nerd, aren't I?) that has incredible music. I never actually did this, but a couple of times I thought about loading up my game, finding a quiet area of space, and go cruising while the music played and I studied.
The only thing I would caution you on with any music, is to be careful to avoid pieces that might be distracting because they are too loud, exciting, or fast. For example, I have trouble studying when something like Ride of the Valkries is playing...
Wisconsin Candidate. NTS 450
BEC - 82 AUD - 85
FAR - 83 REG - 71, 86