Within a couple hours Lake Pleasant is probably the best. Just a short drive north of Sun City West.
For your AOW, (PADI?) check with Academy of Scuba on I-17/Dunlap or the Sports Chalet store on I-17/Happy Valley Rd. Both are almost on the way to Lake Pleasant where you'll likely do your dives. Both also have a pool on-site. List with contact info:
http://www.scubaboard.com/forums/so...90-arizona-lds-list-last-update-9-2012-a.html Lake Pleasant is cold water diving also as it's mountain run-off fed.
I don't dive at Lake Pleasant so others can provide more info but a lot of the diving is done at Vista Point. There's a Thursday night dive that starts up again March 7th, more info can be found in this forum's stickies or at:
Thursday afternoon Dive
People also dive Lakes Apache, Saguaro, Canyon or Roosevelt east of Phoenix. They'd fall within the 2hr. window. None of them are great, they're typically shallower and the viz can be poor (lots of boat traffic) I've dove Saguaro once in decades of living here and don't feel like I've missed much.
If you get out to Mesa (SE Metro Phoenix), stop by El Mar, IMO they're the best shop in town for gear selection. Academy of Scuba also has some good programs/gear. If you're interested, Nitrox.com is one of their affiliated businesses - do the online and you can get a Nitrox Card with a 1/2hr. visit to one of their shops. They also teach the full PADI Nitrox class. I think their store on East Bell is the bigger of their locations. Scubajcf here owns it.
The newest shop in town is ScubaPros of AZ. They just opened recently in a new facility. They're an SSI shop and are one of few ScubaPro Platinum dealers worldwide. (afaik there's about 50) So maybe worth a stop - you'll drive by on the 101 at Peoria regularly. Definitely the closest for tank rentals from Sun City West - literally about a mile or two east.
If you're interested in weekend trips, the Kelp Forests off San Diego or Catalina Island are about as good as it gets. LA/SD is a cheap hour flight on Southwest. Both shore diving at LaJolla Cove or local boat diving. Los Coronados Islands are decent shallow diving south of San Diego, either by day boat or weekend liveaboard. Note that you'll need to arrange a buddy/instabuddy or rent a DM, DM's on SoCal boats stay on the boat.
www.divebums.com for more info.
We also dive the Sea of Cortez from here - about a 1/2 day drive.
San Carlos, Sonora, Mexico Diving In April it will just start getting warmer.