Pandora, the great music disovery service and player, is now offering a free version of its service.

Pandora has hired 30 musicians who have spent years analyzing 400 attributes of songs, like melody, rhythm and vocals. They’ve analyzed over 10,000 artists and 300,000 songs to date. Users pick a band or song to get started, and create a “channel” based on that type of music and which you can stream over their site in high quality audio. Over time, by telling Pandora whether or not you like a given song, the channel will evolve. You can share these channels with other Pandora users.

For more information, see our profile (one of my more effusive) from August 20, 2005.Pandora launched nine weeks ago.

Before today, Pandora charged $12/quarter or $36/year after a 10 hour free trial. Now, users can choose between a free, ad supported version of Pandora, or choose to pay for the service without ads.

Users who have paid for Pandora previously will have the option of having their money refunded, or an extension added to their subscription. Quarterly subscribers will have a year added to their account, and yearly subscribers will have two years added.

Pandora has also added new features, including a favorites list, increased feedback functionality for tailoring stations, better playlist generation and dozens of other minor tweaks.

Pandora has 1 million stations based on 70,000 unique artists or songs.