I've ordered live rock from Tampa Bay Saltwater and Live Aquaria before. I was happy with both. Salty Critter is another place that a lot of people say good things about.
+1 BRS. Get the Pukani rock, it rocks! Or i think the other one is marcosrock.com? Dead rock will become live rock in about year (correct me if I'm wrong please!)
and is much cheaper since you don't have all the water weight.