These are some places that stood out.
We had Lonely Planet dive guides for US and British Virgin Islands and elsewhere referred to the 3 volume Complete Diving Guide to the Caribbean by Colleen Ryan & Brian Savage.
St Croix is about 30 miles south of the rest of the Virgins which, being on a bank, offer sheltered sailing but so-so diving. St Croix is different. Along the north coast there is excellent wall diving quite close to the shore. At Cane Bay it can be reached from the beach.
We spent a week anchored in Salt River Bay and dived the walls just outside the bay entrance. As our compressor was out, we filled our tanks at Anchor Dive Center in the bay.
We spent another week off Fredricksted at the west end of the island. The wall is too deep here so there are mostly patch reefs, but there is also the remains of an old pier that provides excellent day and night diving. There are several sea horses on the pier as well as many other interesting critters.
Finally, we visited Buck Island. This is a National Park that has a self-guided underwater (snorkeling) trail. It also has a couple of interesting dives through huge piles of ancient staghorn coral.
Saba is a tiny island a few miles south of St Maarten. It is so steep-to that there is virtually nowhere to anchor. The entire coast is a Park and visiting boats may only stay on moorings. Visiting divers may only dive with a local dive operator. We dived with Saba Deep who picked us up from our boat each day. The first dive was a small pinnacle with its top at 90' - about 12 minutes bottom time and a dive computer in deco. The other dives were shallower and quite variable; rocky cliffs close to shore and small walls. We saw frogfish and sea horses. After a few days the weather deteriated so we had to leave. There is no shelter.
St Eustatia is another Dutch island quite close to Saba. It's a little bigger and has some shelter but also protects its reefs well. Here we dived with Golden Rock Dive Center. The diving was varied and very good. Again we saw frogfish and sea horses. Off the town is a 'muck dive' where we saw some Flying Gurnards.
Martinique was our standout dive destination of our 2006 cruise. The diving was really very good. There are a number of safe bays on the southwest coast where we could anchor and dinghy out to nearby dive sites. We saw toadfish, frogfish, sea horses and much more. We also dived at St Pierre at the northwest part of Martinique. This is a more open anchorage so we had some problems with swells. There are many wrecks in the area dating from a major volcanic eruption that destroyed the town but our best diving was under the pier.
Guadeloup was almost as good as Martinique. Halfway along the west coast is a Cousteau Marine Park that has a lot of large fish in it due to the ban on fishing there. There's a bronze bust of Jacques Cousteau on the bottom in 30' and you can wave at the glass-bottom boats as they pass by to see it. Some beautiful islands off the south of Guadeloupe called Les Saintes also have some good dive sites.
St Lucia required us to dive with a local guide. Through the Pitons Marine Park we located a licensed guide who came with us in our dinghy. This made the diving more affordable. It was good but not great.
Dominica also required us to dive with a local dive operation. We made a few dives but decided that they were not $70 better than dives we could make by ourselves at other islands. We dived only in the north however. Diving in the south is reported to be better, but the anchorage at Rouseau, the capital, was uncomfortable.
Diving on the west coast of St Vincent was excellent. We had several anchorages available and good wall dives nearby. We anchored once in a tiny bay where we could dive off the wall from the boat - day and night. The Grenadines have some good dives (Bequia, Mustique, Tobago Cays) but generally the visibility, and the majesty of the underwater terrain, did not match St Vincent.
The visibility was poor around Grenada everywhere we anchored. However, there are some islands half way between Grenada and Carriacou called Iles de Ronde. From there we could dive some steep rocky pinnacles called The Sisters.
At the end of our 2006 season, we returned to Trinidad via Tobago. Unfortunately, the visibility was poor and the currents were very strong so we did not see much. We could not dive Speyside at all, which is said to be the best. Reportedly, the diving around Tobago can be very good with many unusual species there from South America. Visibility around Trinidad is always poor due to the outflow of the Orinocco, and this is what affects Tobago too.
Other islands we dived in 2005 & 6 were St Thomas U.S.V.I, various B.V.I., St Maarten, St Barts, Antigua, Montserrat.