There is a Gander Mountain, on 45, just south of 2920 (smallish selection, but close and sells licenses), Cut-Rate has a good selection down on I-10 just west of the loop, Anglers Edge and Orvis on Westheimer, and as mentioned there is a Bass Pro out in Katy.

If he has a boat, there are a lot of places close...lake conroe, lake houston, lake livingston to name some of the bigger destinations. Non boat fishing can be a bit more problematic due to access issues and gators. I don't recommend wading in waters with things that can eat you.

...the only houston club that i'm aware of is [url=http://www.texasflyfishers.org/Main.htm:3eabe]Texas Fly Fishers[/url:3eabe].

i'd just add...that if there is water, and it doesn't dry up, there is strong possibility that you'll find fish in it. I've been fishing in some pretty odd places