We used to live in Houston (well, Kingwood, but that's close enough). For our 1500-sq-ft home (including 400 sq ft garage), our electricity varied from 600kWh in the milder months to 1800 kWh in the summer. Here are the things I considered, although we couldn't afford them at the time:
1) radiant barrier. You can do it cheaply yourself by hanging
reflective film across the framing under your roof.
2) add blown-in insulation. Your attic may be a storage area for you (as it was for us), so you might be limited there
3) roll-down exterior shades. Our single-story home had single-pane windows, and hanging inexpensive shades from the eaves helped the radiant heat noticeably.
4) shade trees (you're already doing this). I tried this, but apparently I have a brown thumb, and the trees died. :(
5) raise the temperature (you're already doing this). We had our thermostat at 76-78. At my office, the "normal" temperature, according to the maintenance guys, was
60-62. I was astonished, and suddenly realized why I (and many others) felt so cold every day at the office. Our administrative assistant actually had a small space heater under her desk that she used during the summers....yeesh.
6) Solar shades. Several people in our neighborhood had them, but I have no personal experience, so I don't know. Another alternative is reflective window film, which applies and works like window tint in your car. Or you can replace your windows.
7) Attic ventilation. Get a ridge vent.
As for solar photovoltaics, yes, it's possible. No, it's not yet economic, if you consider the net present value of the savings, even with the 30% tax credit offered by the Federal Government. Heck, Illinois throws in another 25% tax credit, and it
still doesn't make sense financially. I actually ran the numbers just last week. You'll get more sun in Texas, but I doubt the incentives are as high in the conservative Utopia of Texas than they are in the liberal Utopia of Illinois...