I prefer Damien Rice, Bon Iver and Eddie Vedder (the Into the Wild soundtrack is amazing). They're all pretty relaxing.
I listen to classical stuff too. Or this CD I bought off a band called Croque Monsieur who I saw in Melbourne once. They play traditional eastern European music and stuff like that.
And the soundtrack for the film Amelie (most of which, except for a couple of songs, was composed by Yann Tiersen). If you ever want a CD to listen to while you study I would highly recommend that one.
Yaaay Bon Iver.
I have a playlist for studying. It includes shitloads of post rock, the gloomiest Cure you'll find, the happiest Broken Social Scene/Arcade Fire, Jeff Buckley, M. Ward, a lot of Conor Oberst related stuff, the gloomiest Radiohead, Grizzly Bear, Feist, Interpol, Bon Iver, Wilco.
So basically post rock and indie haha