Last month when we were in Cozumel we went to Paradise Beach... a $12 taxi ride (per taxi not person).
Nice beach, lots of water toys (i.e. float mats, iceberg to climb, water trampoline etc). No charge for the beach loungers, or umbrellas... a $9 pp charge if you want to use the "toys". They also have jet skis and parasailing available for extra cost.
It has decent washroom and locker facilities, and good bar and food service.
Another spot we've enjoyed is Mr. Sancho's Beach Club.