Biosphere has some pretty good ambient albums. I haven't really given a good listen to his music yet, but it is definitely worth a look. Try out the album Substrata first. It is very ambient: the music is built on textures rather than melodies and harmonies.
As for myself, I listen to anything from my library during study, but I usually switch on my cheap logitech speakers and turn the volume down so the music is more ambient noise than anything. I find that if I listen to music with headphones on during study, the music seems too upfront even at low levels. I like music running in the background while I work, but I don't like having part of my concentration consciously or subconsciously diverted because the music is either too loud or too good sounding (which is why I use my bad speakers). To me, it's kind of like the idiom "it's so loud I can't hear myself think" 
