I drive from Houston to San Antonio once a month at least, and we almost always stop at Frank's. Frank's has great food, it's inexpensive and comforting and it's a good location to stop and stretch your legs. I recommend their chicken fried steak, pie, french fries and flavored tea. Don't drink the water, it tastes funny :P The place is never overcrowded and we get good service. They aren't so good at steak, I wouldn't recommend getting a steak unless you want it overcooked- better yet if you want it medium you should order it rare.
Pros: inexpensive, good comfort food, location
Cons: hmm it isn't gourmet?