Shame on you all. Basically if you want the free version, sign up for an invite here which should end up in your inbox eventually (which might be weeks and might be months): http://www.spotify.com/int/hello-america/
And if you feel like paying, you can start immediately, I think.
Spotify has literally (almost) EVERY track available to play instantly, for free.
BUT
For discovering new music, I'd stick to Pandora. Spotify's radio sucks.
AND
Spotify limits you to 5 plays of each track (FOREVER as far as I know), and 10 hours total each month unless you pay for the unlimited or premium versions. (no track limits and 20 hours per month for the 1st 6 months)
I stopped using Spotify the moment these changes were announced.
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Congratulations to BlAcK TuRtLe, the Guru champion for the 2010 GotD.
Been meaning to check that out. After searching some random bands and artists it appears they have some stuff Spotify doesn't have and vice versa. A nice addition to Spotify!