There are a ton of dude ranches in the Texas Hill Country (central Texas). The areas around the towns of Fredericksburg, Kerrville, New Braunfuls, Hunt, Bandera, Medina, etc. abound with nice ranch-type places to stay
Some off the top of my head:
Lazy Hills Guest Ranch
Flying L Guest Ranch
Mo Ranch
The Y-O Ranch
All have web sites... unfortunately, I don't have time to look them up right now...
You might also want to try looking in
http://www.texasmonthly.com for places.