Just got back from St. Croix (August) from another trip there and we can't recommend SCUBA (St. Croix Ultimate Bluewater Adventures) enough. They're easily the best dive shop we've ever been with. Their motto is the friendliest dive shop on earth and they really live up to it. I had emailed Ed back in May and he helped us set up a dive package that included staying at a great hotel, the Palms, and our roundtrip tickets. The price was incredible and you would have thought that at that low of a price it would be a cut rate operation but that certainly wasn't the case.
Their boats are really comfortable and they have two of them, one in Christiansted and the other in Frederiksted so it was never a very long ride.
Their staff is incredible. They did everything from setting up our gear (something that I'd normally not be that comfortable with), to rinsing and storing it for us. And underwater they seemed to know where everything was, including some incredible sea horses. They never rushed us dive and we could dive our computer profiles. When we got back on the boat the Captain was even serving pineapple and handing out bottled water.
I can't say enough good things about SCUBA.