Costa Maya we did Maya Chan's all-inclusive. We booked directly with them. See my notes in the Costa Maya forum on that. There are plusses and minuses about choosing them over other spots for a beach day.
Just did the West End in Roatan. Expensive cab ride ($50 round trip). Look in the Roatan forum for using their bus instead. Roatan is very lush and beautiful. The West End is hopping with beach bars and restaurants. West End beaches are free to use, but you'll pay from $5-10 for a chair (often includes a drink). Bring your towel and grab a spot if you are going cheap.
Belize was ATV riding with cavetubing.com. It was very nice. They took good care of us, as the only people JUST doing the ATV excursion. We got extra special treatment, including a private ride back to port. I feel like we are about "out of things to do" in Belize to make it worth tendering.
Cozumel we used Eduardo's "hire a driver" service and it was flawless. Tequila tour isn't a factory as I'd thought. Just more of a museum and store. Still nice and you get a drink and lots of samples for $10. Ruins definitely aren't much to look at. Our group paid $20 (on top of the $8/pp entry fees) for a guide to walk us through and tell us about the ruins, which was a nice option to have. If you want ruins, though, do them in Belize instead.
Great beach bars in Cozumel. We went to one just west(?) of Coconuts and the food was awesome.
Driver promply got us back to port on time, where we bought sandals (haggle for the price!) and liquor at the Duty Free right at the dock. GREAT welcome back by the Star crew here! Even the hotel director was out dancing on the pier!