http://www.amazon.com/gp/help/customer/display.html?nodeId=201549700
Amazon Echo currently supports the following music services:
Amazon Music
Prime Music (with Amazon Prime membership on Amazon.com)
TuneIn
iHeartRadio
Also:
"If you'd like to add music from your computer to your Amazon Music library, you can import up to 250 songs to your music library for free"