Pandora and Last.fm are two really good places to listen to music online, however both are different services, but a small Greasemonkey script will allow you to publish the music you are hearing on Pandora to your Last.fm account.
PandoraFM is simple. As you listen to music via the excellent Pandora music service each song gets submitted to your profile on Last.FM. You’re listening to music, so why shouldn’t you be able to account for it? Some call it a mash-up, others call it a hack. I call it Pandora.FM.
If you are a Last.fm user and are in a country where it will be available as a paid service, you can check out some Last.fm Alternatives which are free.