My first open water dive was Grand Cayman and it was a great experience. The downside is that the islands are a bit expensive. Easy day dives, nice walls, big and small stuff to see. Plus if you only want to do a couple of dives a day, there is plenty of other stuff to do.
I think that first time diving for an aquarist is different than for 'normal' divers. Everyone that I have introduced to diving that was also into fish loved it and spent more time admiring the reef and the critters than worrying about the fact that they were underwater. I really think it helps newbies relax a bit.
There are some great deals to Fiji, Indonesia, Micronesia and even Hawaii (though it tends to be more expensive due to hotel costs). The reefs are great, the fish life is prolific and there are easy dives to be had, particularly in Fiji.
I would not suggest Truk or Vanuatu or Galapagos to a new diver. The diving there is great, but you need 100+ dives or so to be comfortable with the conditions.
The one caveat about pacific diving: once you've seen the vast soft coral and colorful reefs, the Atlantic just doesn't cut it anymore.
In any case, if you head somewhere tropical remember that you can add volcano hikes, kayaking, biking and many other outside activities to supplement your diving. Eventually, if you like it enough, you'll discover the wonders of a liveaboard. And then you'll discover what being really spoiled is like.
-Rob