Jeff,
I just read another one of your posts (you roll call where you listed all the excursions you are planning)...It seems great minds think alike! We had very similar plans!
We booked the buccaneer catamaran in grand cayman, but didn't get to go because of the weather. We had brought our own gear and snorkeled at Eden Rock instead. The reef was a little hard to find, but once we found it, it was great snorkeling. If you need more information about this as a backup, let me know...I'd be happy to tell you more.
In Roatan we took a discover scuba course and LOVED it! The reef was teeming with life and we saw a Moray eel. We initially thought about going with Salt n Pepper, but I had some difficulty communicating with them and decided to go with Luna Beach (wwww.lunabeachresort). I HIGHLY recommend Luna Beach, but they do require a deposit for a reservation. The resort in the West End at the end of the beach, so it is kind of set apart and quiet. It has recently been remodeled and is just an awesome spot. the dive shop is great with all new equipment. The dive master, Mark, is great and they have a really nice dive boat. Matt and I had a private lesson and then went on the dive with 3 other people who were staying at the resort...we were the only ones from the ship. I took photos of all this stuff if you'd like to see them. Anyways, they had a very nice driver that picked us up, but I recommend getting your own transportation. The ship was 1.5 early into Roatan and we had to get online to email the resort to get an earlier ride. We didn't get to check for a response before it was time to get off the ship (the internet was down that morning), so we got off the ship not knowing what was going on. It was very chaotic and took awhile to find the driver. Once we did, if was fine, but it might be better to arrange your own ride there so you don't have to worry about the ship coming in at a different time. Maybe you could arrange for wherever you go to bring you back to the ship. Our driver took up to a gift shop the cruiseline recommended, Yaba Ding Ding...it was in Coxen Hole, which is not the greatest city...The driver waited for us while we shopped (bought a couple Dive Roatan shirts) and then took us to the ship. All in all, it was our favorite port.
In Belize we did cave tubing with x-stream (www.belizecruiseexcursions.com). There was some craziness with the ship being really late due to problems tendering (high seas)...I will have to tell you about that, but I don't have time right now. Sorry! In the end it ended up working out and we had a fantastic time.
In Cozumel we did some snorkeling, shopping (I shopped for silver, Matt for booze 
), and went to Carlos and Charlies and Senor Frogs. We also went to Pancho's Backyard and some other great places I will have to tell you about. We had a great day there.
I'll try to give you some more info. about Belize and Cozumel as soon as I have more time. You are going to have a great time!!! We have been talking every day about how much we want to go back!!!!!!! We would take the exact same cruise again in a heartbeat.
Robin
