As some posters have noted, you should talk to your dive master and get his impute as conditions at individual sites can change daily. And there are lots and lots of good dives there. But with that said:
3 Really Good Deep Dives
The southern section of Columbia Deep. Columbia Deep is the name given to a large section of reef on the southern end of the typical resort diving area. The area just north of Punta Sur is our favorite section. It offers huge coral formations that rise from a depth of over 200 feet, a portion on a deep wall and lots of crevasses and caves.
Cedral Wall is a beautiful wall with changing topography and excellent fish life. And for some reason, it doesnt get half the diver traffic that some less desirable walls get.
Palancar Horseshoe--Some parts of the shallower portion of Palancar Horseshoe are full of broken coral and little fish life. However, other sections of the area known as Little Horseshoe are a winding maze of pristine pinnacles that rise from a depth of over 100 feet and top out at around 30 feet from the surface.
3 Good Shallow Dives
At Punta Tunich you will find a very quick current over some colorful low profile coral and lots of fish. Sometimes, diving here feels like flying.
Paso de Cedral. This site gets a little too much activity but it's a very pretty dive. Eexpect to see a variety of reef fish, spotted moray eels, grouper, lobster, crab, an occasional turtle and some nice vistas through openings in the coral.
San Francisco Wall. This wall tops out at about 50 feet and the best coral is at 65 feet and above. There is good and varied fish life available and while there is a current, it is usually gentle. All this makes San Francisco a good choice for an introduction to drift diving on a wall.
Joel
http://www.mxtravel.com/cozumel/cozumel_diving.html