Personally I'm a HUGE fan of Superhero Soundtracks on Songza. It's an app that will play songs that match your mood or activity, and the music is great. Superhero Soundtracks is easily my favorite because often time there are no lyrics, it's just orchestral pieces so nothing too distracting.
I play that in conjunction with Rainymood (rainymood.com, it just sounds like rain, it's really precious and great) and I'm busting out paperwork like it's my job... Oh wait. That is my job.
Songza is definitely my favorite listening platform, though. Tons of great stuff.