I recieved an invite to Rdio.com today. So far its the best alternative to my beloved Lala.com yet. While Rdio.com is still invite only at this point, it functions quite well. I also haven't found any issues with their Library. So far anything I've searched for came up. I've even discovered a few new cool bands. But one of the best features yet allows users to sync albums to their iPhone app for offline listening. Just as if you had the album on your iPhone.
So far the only caveat I've come across is that unlike Lala, its not free. Listening online only will set you back $5 a month, while the full meal deal with the offline iPhone listening will set you back $10. However, also unlike Lala, you're not limited to a single listen through a song (however that limitation worked well for me).
So enough chatting about the service, you want to check it out for yourself. Good thing I'm giving away 3 invites. Simply leave a comment to this post stating your favorite album (current or all-time), and I'll pick 3 of the best answers (as objective as I can) and send out the invites.
Have a good additional alternative to Lala.com? Leave a comment or shoot me an email.