You won't find many providers in Houston for single server colocation. Most of the providers won't even talk to you unless you want to commit to at least 1/2 rack. However, I believe Zogmo (www.zogmo.com) and OrangeFiber should be able to accomodate you. Both are located in Houston and provide colocation services.
I have not used either provider, but I would suggest that you run a search on WebHostingTalk to get a "feel" of what your experience might be like.
ColoGuys would certainly be a respectable Dallas option. If you can deal with Dallas as a general alternative, I think you'll find a far greater number of options, which will probably be a good thing in finding a sensible solution for a single server.
Corey Northcutt | Northcutt Competitive inbound marketing with a hosting industry competency. Social | Content | Optimization | Outreach