I've ordered several corals from Ebay with fairly positive results.
I always buy from a seller in Florida for better shipping prices and travel time.
I've had decent success with reefgardner (Johnny & Morgan from Miami), elitereefs, and the exotic reef (tiny sps frags), and piece-of-the-reef (LR from Tampa).
Most (unless otherwise described) are much smaller frags than you would expect to get for the price.
Of course, none of them compare to the great (and extremely generous) frags that I've gotten from local FMAS members both personally and at the end of meeting auctions.
I've also noticed that after I add in shipping a lot of times I could've gotten a bigger, nicer coral for the same or less at my favorite LFS... especially Reef Life, Pets Unlimited, and Eco Reef in Broward.