The problem with this kind of recommendation thread is that people always end up recommending
interesting music (M83, for example), when music that "sits in the background" i.e. "can be ignored by my brain's higer-functioning areas" is often not.
This goes for the "music to sleep to" threads as well.
I'm sure that some people
can study and/or sleep to interesting music; it just seems like a waste of time to me. My recommendation: go
here and find a loop that's sufficiently mindless (there's plenty of interesting stuff there, too, so beware).
Just an observation: in my experience, though I might want to listen to music while I study, and while doing so may increase my enjoyment of said activity just a little, if I were to be honest with myself I get stuff done much more quickly without the distraction (this is, however, in the absence of a greater distraction which might be removed by the music). What we have then is a much greater duration of a slightly less abhorent activity. Simple cost/benefit survey says...