Pacific Scuba - Small group tours. They describe dive sites and certifications, with information on hotel packages. - http://pacificscuba.com.mx
Boca Divers - PADI instruction available, along with dive site descriptions and contact information. [English/French/Spanish] - http://www.bocadivers.com
Chico's Dive Shop - Offers dive trips and snorkeling expeditions, as well as customized tours. - http://www.chicos-diveshop.com/