Go to Cabo and then head up to La Paz (you can take a bus up if you can't arrange to fly in there). There are lots of beautiful islands off of La Paz with great diving. Many large rays. Read Steinbeck's "Log From the Sea of Cortez." Not much has changed since he wrote it. There's a wreck dive off Esprito Santo. If you go in winter you can take the drive over to Magdalena Bay and see the grey whales in their breeding lagoons. Best place to stay is Club El Moro, where for about $50 a night you get large room with balcony, kitchen, nice little pool. Even better is to charter a sailboat there, anchor off the islands and then arrange rendezvous with dive boat. Then you'll get private beaches as well.
Puerta Vallarta has good diving too and I'm sure the other spots do as well, but La Paz has more charm IMHO.
Welcome to FlyerTalk and have a great trip.
[This message has been edited by letiole (edited 08-27-2000).]