Can you tell me what to plant in x-large pots in the direct sun?

I would plant a Palm tree as it will stand up to the sun and give a dramatic look. Follow the rule of designing planters: you need a Thriller, a Filler and a Spiller.

The Thriller (or dramatic touch) in this case is the Palm. The Filler can be any flower that stands up to your heat such as Hibiscus (perhaps). And the Spiller can be a very tough plant that loves sun, Asparagus Fern as it gracefully spills over the sides of the planter.

I always follow the above rule and receive lots of compliments on my arrangements. I live in southern Ontario (Canada) where we have very hot Summers. In late Fall, I hose off my palm tree (to avoid bringing bugs in) and keep it in the living room for the Winter. I do the same with my Asparagus Fern.

Another thought would be to go with a succulent of some kind. They do very well in the Texas heat...and you could do a variety of them in one pot to give you an interesting look.

The best low maintenance plants in Texas, pots or no, are red yuccas. They'll multiply to fill the entire pot. They're heat and drought resistant (once established) and nothing bothers them - not bugs or critters. Plus hummingbirds love their flowers. It's all good!

I am a big fan of purslane, a succulent. It spreads rapidly and on occasion will come back the next year. And it loves heat -- the hotter, the better. I have pots on each side of my driveway and they are gorgeous. Only need occasional watering. Rosemary, salvia, and lantana are also good. I haven't tried red yuccas, but intend to very soon.

moss roses, like sun & low mainteance

I put some purple fountain grass in a pot on my deck and it turned out beautiful. I put a lot of styro foam peanuts in the bottom for drainage. Here is what they look like and they are still growing. I used to plant 4 in front of my garden to hide the garden area. They get really big!!!! This is in the sun all day and I don't water it very often.