Cozumel has one of the best divings in the world. The underwater gardens of Cozumel are formed by great banks of coral, and they are home of a big variety of tropical fish. The divers with most experience (I am not that, I can tell you) say that the submarine experience in Cozumel follows the Great Barrier in Australia, and that is a compliment!!!
The professional diving stores in Cozumel can design you individual packages but Aqua Safari´s services is awesome. I have had some ear problems since I was a kid, but my girlfriend is PADI certified scubadiver, so experience or not you will find the emotion to dive in these fascinating waters.
Aqua Safari has great boats and diving gear, and they have the best trip to the Palancar Reef. The divers must make adjustments for the excursions in advance. In case you are not familiar with the area, many hotels in Cozumel have travel agencies that can make the reservations and plan the transport. JUST TAKE A NOTE OF THIS: half of the people who visit Cozumel come to experience the diving.
The most wonderful sites are in the south of the island. By far the best spot is Palancar Reef. The Palancar Reef is one of greatest in the world, and it is considered one of the best places to dive in the northern hemisphere. It's about 2 miles away from the beach and you will find the mixture of four different coralline reefs, gigantic sponges and incredible under caverns that will be delight of the tour! This place was brought out to the world by French diver Jacques Costeau. Trust me this will be a highlight of your Cozumel experience!!!!