Grooveshark is awesome! I started with Pandora but got sick with all the limits. Been using it for about 3 months and it is my favorite service by far!
Taking this off my friends Blog (Bioware QA Designer!), He found an awesome music service called Grooveshark, read the post for a description. It has EVERYTHING!! http://notme2000.blogspot.com/2010/02/grooveshark.html