My favorite place is Playa Sol. It's a beach-like resort. You can take a taxi there from the pier ($14) and it costs $8 to get in. They have floating mats, hammocks, chairs, etc. They offer food and drinks for sale. You can also for an extra charge, go parasailing, rent waverunners, get a massage on the beach. They have a lot to do and its a fun place to spend time while in Cozumel.