I typed in "Anya Marina" and it came up with an extensive list, so it automatically wins in my heart. In fact, that's how I judge all music-related sites, by amount of Anya content. Anywya, you can add songs to a playlist, and it's free. Ace. The giant ads are obnoxious, but who am I to quibble with free music?
From the website:
"Do the artists get paid?
Songza pays for licenses from all the major performing-rights organizations (ASCAP, BMI, SESAC), who then pay the publishers and writers in proportion to the number of plays they get on Songza.
The music streamed on Songza is generously made available by sites like YouTube.com and imeem.com, who in turn pay the rights owners for use of the songs."
(From Metafilter, in a post stating that Guitarist Joe Satriani is suing Coldplay over Viva La Vida (audio). Satriani's version: If I Could Fly (audio). Favorite comment from the thread: "After a series of close examinations, I can confirm that both are terrible songs. posted by stresstwig")