Depends on what part of Houston you are in, but here's some shops:
Gander Mountain on IH-45 North in Spring. It may be a bit of a hike but they have a pretty large SCUBA area with a good selection of items from multiple manufacturers with very good prices and a helpful, knowledgeable staff (from what I hear all three Houston Gander Mountains have a dive section). There are some good shops in Houston but you'll probably have to drive a little for some better service.
Gigglin Marlin - Never been to their shop but want to, I did meet a couple of their employees/divers diving at Aquarena and they were really nice.
Hydrosports - the dive shop in Lake Jackson for Mammoth Lake, Brand new store Pictures look great.
WW Diving - Another little hike to Humble, this shop comes recommended from a good friend of mine, and I think they handle tech stuff. (yet another I would like to visit.)
Kickady SCUBA - is in the Woodlands and is run by a really nice family that just loves to dive, and they have a Tiki-Bar IN THE SHOP!!!
Houston SCUBA Academy - I'm pretty sure this is the oldest dive shop in Houston, I got certified through a sister store (now defunct) back in 1989, there still in business so they must be doing something right, good size store and they're a Scubapro dealer (best regulators in my opinion.)
Scuba, Inc. -
http://www.scubainc.com/
Scuba Houston -
http://www.scubahouston.com/
Also check out the
City Of Houston Underwater Mariners Social Diving Club - or CHUM for short, a great group of fun loving divers in the Houston area who dive a lot and have monthly drink-er-I-mean meetings at the
Stag's Head Pub near downtown.
For Houston Diving there is
The Blue Lagoon, North of Houston near Huntsville.
South of town there is
Twin Lakes, off Hwy 288, and Further South is Mammoth Lake, (see Hydrosports Above.)
Besides, Lake Travis, for Central Texas there is Canyon Lake outside New Braunfels, Diving there is usually off North Park, Aquarena Center in San Marcos, The Comal River in New Braunfels. Heres a link to
Dive Site List from the Texas A&M Scuba Club website. Heres another
Texas List with some links, has some of the same info.
Water temps in May are usually Mid to upper 70's I usually dive a MM wet suit all summer. Hope this helps.