Otherwise this would turn into a regular list of Houston restaurants, which is being done by other people already. Italian restaurants usually have a tomato or mushroom sauce that doesn't have meat in it. Some pizza restaurants use sauce and crusts that are vegetarian or vegan. Most Chinese restaurants have a few vegetarian dishes. Most Thai restaurants have a few vegetarian dishes.
Most Indian restaurants have a lot of vegetarian dishes, usually heavy on the dairy products.
People always suggest that Mexican or Tex-Mex restaurants must be great, what with all the rice and beans and things. Sometimes this is true, and if you eat dairy you can usually get a cheese enchilada. All too often, though, beans are made with lard, and rice with beef or chicken stock. Some places fry in lard, too. The Author is not a vegetarian, but intends to become one some day, and frequently chooses vegetarian meals.