We booked a private driver and guide to go to the Appleton Rum factory through realtours Jamiaca ("Chuck" Norris). It was about $300 but worth every cent.The guides were amazing - they explained the local culture, schools and even showed us some off the beaten path sites - including two "benches" in a town that really old graves. The rum factory is worth it as well. On the way back, we had some extra time, so they gave us a highlight tour of Montego Bay and stopped at their favorite Jerk joint. They kept us away from the crowds and gave us an excellent day.
We booked a private stingray/snorkling excursion with Cayman Eco Adventures. They were good - we got exactly what we were told would be included and we got to the Stingray sandbar before most other boats so we had a better experience. The reef snorkling was okay. The whole exercusion was only short of 3 hours - we would have preferred a long tour, but there were only 9 people on our boat instead of the 25-50 on every other one.
We did our usual thing in Cozumel - we had lunch at La Conchita del Caribe (the best seafood place in Cozumel - $35 including tip for appitizers, four beers, two entries (an entire fish and a plate of huge shrimp) and dessert) - it's just outside of downtown but a cab will take you for the same price. Then we went to a local (not tourist) liquor store and bought tequila to bring back.