Ahhh, great great question.
I've looked hard over the place for years in search for great music for studying. For me, established by the tried and tested route, it was important for this music to satisfy certain criteria. We all would have different moods when studying and it's important I felt for the music to suit the mood. As an instant marker, vocal music was really a no-no at all instances although a few soft backing vocals here and their did no harm
For when I was bored/tired in my studies I'd want music that was uplifting. It should rekindle my interest in the maths infront of me so i'd need music that was fast paced, rythmic but not too interesting or something that needed to be listened attentively to. Some progressive smooth trance like armin van buuren's 'a state of trance' albums are good as too are to are a couple of ATB albums. Away from trance I'd like OST music like that from the game 'assassins creed: brotherhood' or, in more instances movie sountracks. I don't like the overplayed 'the dark knight' soundtrack actually but a lot of other sound tracks from it's composer hans zimmer are awesome. 'King arthur,' 'Angels and demons' and even 'The island' are great OST albums that I have. I think one or two of them might not be hans zimmer's work, not sure, don't matter.
Actually, you migh find some acoustic material quite good for this purpose too, like from the artists Ah nee mah or Nicholas gunn.
When I was interested with my work I'd sometimes try and work in silence- though not always as somehow, for some horrible reason, I'm always put off by the sporadic yet perpetual stream of disconcerting sounds that london throws up, weather it be in the library, my room, in the exam hall, on public transport, londons always ****** noisy!!
So I'd still need to use closed headphones and listen to tunes often, even when It wasn't going to benefit my studying. Music from the genre of new age was good for this with special preferance going to amethystium's albums as well as some of the later ones that mike oldfield has released (like 'light and shade' or 'music of the spheres'). Ryan farish has
Lastly when i was tense and anxious like before an exam or near (enough) to a deadline I'd listen to classical or ambient. With ambient there's stuff like from liquid mind or matt fink that are very light and smooth, instantly calming- especially before bedtime. You could also try completely natural music like 'echos of nature: the natural sounds of the wilderness' which has ocean, bird and other noises from nature. Quite nice really.
With classical there's quite a lot out there, although I'd avoid stuff with a too large of a dynamic range. You see, a lot of the passage might by very quiet, then suddenly there's a crash crash crash of symbols or whatever!! NOT good for reducing tension I have found from experience. A great album is 'The 99 most essential relaxin classics' which is only available on amazon. There's 100 tracks here available for around £6 I think (amazon mp3 store) and it's a great buy. Another real great composer is one that's overplayed a bit, but great for this purpose- ludovicio einaudi. It's smooth it's relaxing and comfortable (giovanni allevi is less so for example). Einaudi's later work is best I'd say, especially 'Una mattina' (among my most favourite albums of all time). A last suggestion is for one album I particularly like in the genre of jazz 'Charlie haden & pat metheny- beyond the missouri sky.'
You might read the above and think 'this guys a freak'. Fair enough!
There might be some of what I mention that you may find helpful but most of it won't apply at all. I mean not only are musical preferences between one headfier and another wildly different but so too should be school/university/further level studying habits by the very nature of this activity. I just thought I'd share my experience with sound and studying.