Is there something specific you would like me to link? I'm really not exaggerating when I say the web is overflowing with this content. I could link some of the "big" names, but for every one there are dozens or hundreds of similar sites. It's never-ending, especially since almost every indie artist/dev promotes other indies.
Don't forget http://www.ektoplazm.com/ . Completely free music, mostly psytrance and dance, 100s of cds worth, you can't even buy it if you wanted. Lots of it is very good. The business model for artists seems to be to release free music and get yourself promoted enough that you get invited to DJ at electronic music festivals. The record sales are total peanuts so why even bother. The site crowdfunds redesigns and such but mostly people work on it because they really like the music.
Don't even need to restrict yourself to indie. I've got a Spotify Premium account that my wife sometimes hijacks to listen to at her business. Since you can only listen on one mobile device at a time, I'll just hop on Grooveshark if she stole Spotify. I've never not been able to find what I was looking for on Spotify on Grooveshark, and often it has songs in the catalog that Spotify does not.
Beyond the other links, alt-music is out there and can be very good. E.g. http://www.ocremix.org/ (which makes free remixes of video game music, often in ways that add a ton of musical value above and beyond the track being covered).
https://bandcamp.com/
http://www.jamendo.com/
https://soundcloud.com/
http://freemusicarchive.org/
http://itch.io/
http://www.gog.com/
https://www.humblebundle.com/
http://www.indieroyale.com/
https://libregamewiki.org/Main_Page