In Cozumel, I think we will be going to Paradise Beach again - we love it there! It's free entry, a bucket of beers is $15, and for $10 you can use all their water toys (snorkeling, kayaks, floaties, etc).
In Grand Cayman, we plan to take a taxi to 7 Mile Beach and snorkel and lounge around...we have done the Rays, Reef and Rum Point excursion through Nativeways before and I highly recommend that if someone is looking for an excursion.
In Roatan, we have a tour booked through Victor Bodden for an island tour, beach, shoping, and to see the monkeys. $30 pp inclused our own private driver for the day to take us anywhere we want. He comes highly recommeded and its cheaper than taxis!
In Belize, we are going cave-tubing through Major Tom's. I have wanted to do this for years and am really looking forward to it.
Feel free to join us on any excursions (we do have to reserve ahead for Belize and Roatan to ensure space is available, but we don't pay til we get there).
I am very jealous that you will have already been on the boat for a week Gino! The Eastern itinerary is my favorite - what are you doing at St Thomas and St Maarten?
Have a great weekend all!