Thai Village (Lincoln Village shopping center 290/I35 same parking lot as Gold's gym) has the best Tom Ka soup I've ever had. Every person who tries it tells me how great it is. If you don't like it, your two favorite football teams are OU and Notre Dame.
San Francisco Bakery (Anderson Lane and Shoal Creek next to Steanmart) has REALLY GOOD french onion soup. Its cheap too.
Tortilla Soup at Houston's is ridiculous. I could eat it everyday. Of course I would look like Gardner Barnes, but whatever. It's not traditional tortilla soup as it is heavy and creamy, and dreamy.
I don't think I have ever been disappointed with Austin Java Co's soup of the day, but the Chicken Enchilada or Mushroom Curry are my favorites. Plus, they have the Smoked Gouda Bacon Burger and arguably the best Bleu Cheese & Peppercorn Burger in town.