I currently identify as mostly vegan/strictly vegetarian. Even if you aren't yourself vegetarian or vegan, please read on so that you can better accommodate the restaurant-choice-buzzkill vegetarians and vegans in your life.
1. Via 313
Via 313 serves genuine Detroit-style square, deep-dish, hearty "The Marinara" pizza (no cheese/vegan) which makes me do a happy dance every time I have it. Via 313 also offers a house salad and roasted broccoli & cauliflower that happen to be vegan and delicious. Via 313 is great for dining out or carrying out with omnivore friends.
2. Mr. Natural
Favorite dishes at Mr. Natural include the Potato Flautas and the Mr. Natural Burger. Mr. Natural also serves some of the best vegan baked treats I've ever had. I would not bring my omnivore friends here, because the ambiance is a little lacking, and it might be a bit funky for the uninitiated. That said, I'm thankful for Mr. Natural blazing a trail as one of the old guard vegetarian restaurants in Austin.
Guero's offers a separate vegan menu that you can request at the host stand. Chad and I love everything from that menu, and return often. I love that this definitively-Austin institution on South Congress Avenue embraces vegan diners. We can go here with omnivore friends, and keep everyone happy. Guero's is my perfect dining destination for atmosphere, great food and drinks.
4. Bistro Vonish
Bistro Vonish is elevated vegan cuisine served from a trailer to tables under a large event tent strung with lovely bistro lights. On cold nights, a fire pit offers some warmth. On hot days or nights, large oscillating fans on stands offer some relief. Everything Chad and I have eaten here is really delicious and served with a perfect balance of flavors, textures and visual-appeal. I especially like the butternut squash hushpuppies (seasonal), the BBQ seitan sandwich, and the french toast with home fries and a side of seitan available at brunch time on Sundays. Bistro Vonish is my favorite all vegan restaurant in town. I hope Chef Craig is able to transition to a brick and mortar restaurant sometime in the near future.
5. The Beer Plant
This place is expensive, almost always crowded and almost always deafeningly loud. The food is great though. The crowds and noise are the price of popularity. Chad and I have been here with omnivore friends who reported that they loved the food. As indicated by the name, there are also an impressive number and variety of beers on tap.