The founders of the Kazaa P2P program are back in the music download scene with the launch of Rdio, a legal music streaming service. The service offers per-track streaming from the web and on mobile devices for a fee. The iPhone and BlackBerry mobile apps are already available, and the Android-version is also on the way. Interesting features of this new service are that users will be able to share what they’re listening to with other folks, see the top songs on the network and easily stumble upon new music. The basic web-only service will set you back $5/month, though you’ll be able to pay $10/month in order to get the service on the web and on your mobile device. With big music labels such as EMI Music, Sony Music Entertainment, Universal Music Group, and Warner Music Group joining the act, they’re able to offer a catalog of a good five million songs, which is a juicy number of songs to go through.