I also live in Texas, and my A/C also has trouble staying below 78 some days. I usually put my fermenter in a fridge or freezer with a temperature controller. When they are all full, I will put the fermenter in the tub in my guest bathroom and fill it half full of cool water. I put a T-shirt over the carboy and pour water over the shirt every once in a while to keep it wet. This should cool the fermenter by 5 to 10 degrees below room temperature. You can cool even more by periodically adding ice to the bath and also by setting a fan to blow on the fermenter. If you don't have a spare bathroom that you can dedicate to brewing, you can find a large plastic tub at your local hardware store that works as well. Make sure and put it someplace where the air will circulate around it (i.e., not in a closet).
Alternately, you can try to make something that does fine at really high temperatures, like a saison.