The new issue of
Scuba Diving magazine at the newsstand (issue date June 2007) is packaged with a special one-shot mag called
Dive Into Adventure (you can't miss it; Kelly Hu is on the cover of the special in her dive gear --- yum) and that one-shot should have most of the information you're looking for. The book
Scuba Diving & Snorkeling For Dummies also has a lot of solid information and comes with a very good CD-ROM produced by the Professional Association of Dive Instructors.
Here's a few links that might help:
http://scuba.about.com/od/instructioncertification/tp/scubacertfaq.htm (definitely read that first)
http://www.scubadiving.com/find_a_dive_shop
http://www.naui.com/
http://www.ssiusa.com/
http://www.padi.com/padi/default.aspx
Also,
Scuba Board is a good community site.
It probably doesn't matter which of the three organizations (PADI, NAUI or SSI) your instructor is affiliated with. Most YMCAs offer scuba courses in conjunction with PADI; Scuba Schools International instructors are all affiliated with dive shops, as are NAUI instructors, and (where I live in Florida) most of the better dive shops seem to be affiliated with SSI. That said, your key factor for picking a class should be how good the instructors are and your comfort level with them, not one bowl of alphabet soup over another.
I'll be honest here: I'm not at all fond of PADI; as a rule, it seems more interested in wringing money out of its members than the others (for examples, see any issue of
Sport Diver magazine). As the old joke notes ...
Three instructors were out on a dive boat with students off North Carolina last fall. The boat hit a log that punched a hole in the hull and the boat began to sink because the bilge pumps couldn't keep up.
The SSI instructor ran around telling his students to grab everything and jump overboard.
The NAUI instructor said, "Yes, get your dive gear but put it on and use it as a life jacket."
The PADI instructor agreed with the NAUI instructor and said, "Yes, put on your gear BUT bring your credit cards - we're going to make this a wreck diving class!!!
