Don't miss the Swim with dolphins at Chankanaab Park on Cozumel. You can book direct with
http://www.dolphindiscovery.com it is a fantastic day- we did the Royal Swim and it was unforgettable.
an expensive day but worth it.
Shop at the Forum shops then have lunch at Pancho's backyard, a nice place with lots of leafy courtyards, Mariachi band playing and good food. Prices are good too.
We enjoyed Jimmy Buffett's Margaritaville restaurant/bar- you can sit on one of the decks that lead down to the ocean and watch the waves crashing against the piers.... great place.
Have a look at
http://www.Cozumelinsider.com you will find lots of interest here- I used it a lot.