That's a pretty vague question.
You have two options, get her something she likes, or get her something new that she might like.
Being that I don't listen to MTV, nor do I suspect most of the people on this board do, I would find it hard to make a judgement on what to get her. So I can't make those recommendations.
Girls generally like it when you get them something they are interested in. It shows you pay attention. Pick up on the hints ect ect... If you don't know her very well, but would like to, I'd say take this route.
If you know her well already, broaden her horizons. Get her some vivaldi or bach
Or some Tool (wo0t for Tool).
You could always play it safe and get her a gift certificate to a Music shop. Go with her and TRY and pick something else out. If she doesn't go for it, at least she got something she wanted. But, that takes all the thought out of it... and that's what counts.