This thread topic is too good not to revive, so since Cat gave me permission, I'm going to bring it back from the dead.
For me, music is an absolute must when it comes to studying or just getting shit done in general, but it largely depends on what type of music I'm listening to. Specifically, predominantly instrumental music that features notable rhythmical interplay, with calming (or just not 'in your face') sentiments tends to work really well for me. Examples of artists that have a lot of music like this include toe, how to count one to ten, and haisuinonasa. There's something about different instrumental sections combining in such a precise way to create something that's holistically greater than the sum of its parts that puts me in the perfect mood for being productive myself.
The other type of music that I find can be rather helpful has already been mentioned by Sai and Cat, namely IDM. For example, artists like Solar Fields and Ametsub tend to be extremely effective. Once again I find that the most important thing is that the music has to be calming, but not in that sort of 'putting you to sleep' sort of way; rather, I need it to be calming enough that I don't get particularly stressed nor overly distracted, but 'active' enough that it keeps my brain subconsciously processing things.