I'm not digging for gems in indie genre, mostly play popular ones if I like them. So you probably know about those gorgeous soundtracks, but here we go anyways:
Crypt of the Necrodancer has pretty good soundtrack, however, on steam (and gog) you can find "extended soundtrack" which is, basically, 2 remixes/covers. I myself love one called "Aria's ascent" by FamilyJules7x. You can get it without associated game here: https://familyjules7x.bandcamp.com/album/arias-ascent
Second one is Undertale's soundtrack. Great game with a great music. https://tobyfox.bandcamp.com/album/undertale-soundtrack (some of the most amazing tracks are hidden, like megalovania)
Third one will be PAYDAY 2. Game is shite now, but ever-so expanding soundtrack is still amazing. Haven't found it anywhere else, so here is steam link: http://store.steampowered.com/app/254260/
PS: registering on the forums sure is a hell of a challenge... Second try, yeah!