If you want tomatoes that set and bear fruit in Texas' summer heat (at this writing we are expecting yet another triple-digit day), you can hardly go wrong with cherry or grape tomatoes.
In my garden the Juliet (Lycopersicon lycopersicum), which is somewhere in size between a grape and plum tomato, is a real champ. I even put the plant into the ground toward the end of April, which is terribly late for Central Texas, and it is still prolific (as you can see in the picture).
While I like to grow heirloom tomatoes, I also like to keep hybrids like Juliet in the mix, for dependable production. This tomato is not sweet like cherry tomatoes and not as juicy as grape tomatoes. In form, texture and taste, it reminds me more of an Italian plum tomato.
I've been picking them before they are fully ripe, but with a heavy blush, trying to beat the mockingbirds. They ripen nicely on the kitchen counter in a day or two.
They're great as snacks, in salads and salsas.