There's a number of fields around.
Tank's out in Katy
TXR up in Cypress
Twisted Texas up near Conroe
Zone North up by Interconenental (probably the closest decent field)
Zone South down 45
J5R up on north 45.
Best place for some quick research once you're in town is Pro Edge Paintball. As far as I know they're the only independent (IE not on a field) Pro-shop in town: Pro Edge Paintball Houston,Tx | Pro Edge Paintball
I'd stay away from Paintball Bonanza and Survival games of Texas. I've never heard anything good about either of those.
There are a couple of smaller fields in town, I just don't know anything about those.