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Maybe: http://bitnami.org/stack/wordpress#cloudImage I'd lean toward 32-bit Ubuntu if you want to avoid issues, but 64-bit if you are thinking long-term maintenance. Even though 64-bit should work, in my experience dealing with 64-bit for simple stuff ends up being more of a pain than it is worth. Of course, I'll probably get downmodded for saying this.

See also: http://aws.amazon.com/amis