Now available in the US!
Free accounts are still invite-only, but you can use this cheat:
How to Get Spotify Free Without an Invite
This is a
very impressive service. Sure, they don't have all the rare crap we usually listen to, but for all that "novelty" music that you want to hear once in a while, it's a great service.
The free service has occasional ads, but for $10/mo you can get rid of them, and enable iPhone support as well. Good stuff.