I second (or third, etc) many of the suggestions above, particularly Bouldin Creek Cafe and Eastside Cafe (yum). Also, for Mexican, I highly recommend the veggie tacos at Habenero. They've got poblanos, tomatoes, onions, squash etc all happy together in a spicy gravy in a warm tortilla. Either that or their migas are a great alternative to the cheese enchiladas vegetarians are otherwise often stuck ordering at Mexican restaurants.
It depends on what you're looking for.
I've lived in Austin almost 3 years, and as a vegetarian, I rarely have trouble finding something good to eat.
One of the best meals I've had here was a veggie tasting at Wink, but it was pretty pricey.
Wink, Uchi and Vespaio are pretty solid high-end choices. Aquarelle has some veggie offerings, too.
I mostly eat at low- to mid-range restaurants, though.
I love Enoteca, the sister restaurant of Vespaio. It's much less expensive, and there are plenty of vegetarian options, like the tagiatelle con funghi, and great panini, not to mention some of the best fries I've ever eaten.
Titaya's in my favorite Thai. They're good about being veg-friendly, and the food is always really fresh and delicious, and the desserts are amazing.
East Side is good, too. I love taking out-of-town guests there.
Blue Dahlia is nice for sitting on the back patio, sipping iced tea and eating pretty good sandwiches.
Have you thought about tacos? TacoDeli and Torchy's are inexpensive and pretty Austin-y. The Dona sauce at TacoDeli is worth the trip alone.
My favorite fully vegetarian place is Bouldin Creek Coffeehouse. It doesn't look like much from the outside, but the food is really good. It can be crowded during peak times, and especially at weekend lunch, but the wait is worth it. I almost always get breakfast, and it's pretty much for the potato hash cakes - they're crispy and brown on the outside, and fluffy and soft on the inside. So good.
As a vegetarian, I'd recommend Wink, Uchi, or Vespaio for higher end dining. Wink will make anything on the spot for vegetarians, just tell 'em what you do and do not like. Uchi has a few vegetarian items that i really enjoy, although i really don't like what they've done with the sunomono salad lately. Vespaio has that funghi con polenta appetizer that they must try, although it can be inconsistent at times.
In addition, I'd take 'em to Buenos Aires Cafe for the gnocchi and veggie empanadas while you can try some other dish. Vietnamese is a good option, specifically Sunflower or Le Soleil for best eggrolls and spring rolls in town amongst other vegetarian items. I had terrible banh mi in New York last time I was there, so Baguette House, Tam's Deli or Pho Van (tofu banh mi can be requested even though it's not on menu) could be a good contrast for them. Madam Mam's has some good Kao Soi and Tom Khlong, although the latter does have a little fish sauce in it...
As for the other recs on this thread, I'd stay away from Veggie Heaven, they can find much better vegetarian asian food in New York, plus i don't like americanized chinese food... I've only been to Mr Natural's once, and it's merely okay. Eastside Cafe isn't a bad option, nor is Swad (good Indian street food appetizer stuff, okay everything else). I'm not a fan of purely vegetarian restaurants, so don't care for Mother's that much. But if your friends are vegans, then yeah, you probably SHOULD take them there.
and PLEASE don't take them to Ruby's BBQ, as previous threads would suggest. i can't stand the vegetarian items there.
East Side Cafe is definitely on that list. And...
Mother's Cafe has a vegetarian menu and I've liked everything I've had there. I hear that Daily Juice Cafe has good veg and raw prepared foods in addition to juices. Mr. Natural is veg and has a following, but I've never eaten anything there to write home about. Bouldin Creek Cafe has some great veggie chorizo breakfast tacos. For salad, I've heard that Leaf is pretty delicious. And I think Hut's has the best veggie burger in town. Oh, and I took a friend of mine to Izzoz Tacos for their fried avocado taco, and he rated it in his top five favorite foods ever!
I've worked across the street from Veggie Heaven for 5 years and I've eaten there twice. 'nuff said.
Mr. Natural is okay, but I agree with the comments about it above.
Eastside Cafe and Uchi are really good and I agree with the others.
I personally really like the vegetable plate at Vespaio. It's not cheap (high end Italian) but I'm an omnivore and tend to get the veg plate there every time I go because its so freaking good.
I'm a big fan of Swad. It's 100% vegetarian Indian. It's Indian street food mostly, but its soooo good. I usually get the appetizer that has about 8 little samples of dishes on it for the whole table to share. That and another dish is more than enough for 2 people.
Other places you can get pretty decent vegetarian options: Galaxy Cafe, Mothers, Lux (sandwich shop with a killer tofu sandwich), Cippolina has some decent options, Flying Falafel and Po Boys, House Pizzeria (potato and rosemary pizza.. yum), Mrs Johnson's Bakery (yeah, its a donut shop but i hear its vegan because of the owners and oh my are those donuts good... opens at 8pm though), Cissi's Market has good veg options, Sugar Mama's cupcakes does a couple good vegan cupcakes, Cafe de Bella does a good tofu sandwich, San Francisco Bread does a good vegetarian sandwich, Magnolia and Kerby can be vegetarian friendly..
hope that helps
I am a vegan Austinite and consider myself a resident expert on local vegetarian cuisine. If you are looking for a vegetarian restaurant, I strongly suggest either Veggie Heaven (asian) or Mr. Naturals (mexican). If you are looking for a restaurant with vegetarian options for your friends and meat for you I recommend Curra's Grill, they have some of the best Mexican food in Austin and are VERY veggie friendly, or you could always go to Dog Almighty or Terra Burger for a veggie-dog or a veggie-burger. I would also recommend Trudy's tex-mex or Titaya's Thai Cuisine.
I disagree with the recommendation of Veggie Heaven or Mr. Natural. When I lived in NYC I had the best of the best in asian vegetarian cuisine and Veggie Heaven just doesn't add up to what they would get in an average Chinatown or Koreatown joint, plus the service sucks. Mr. Natural is pretty filthy and has failed health inspections and word is that there are secret shortcuts in the food (i.e. not strictly vegan).
For a casual meal, I second East Side Cafe. It's casual with fresh veggies. For higher end dining, take them to get some fab vegetarian sushi at Uchi. I ate there as a vegan and was super happy with my rolls and noodles. Or bring em to Paggi House! Seriously good (http://www.paggihouse.com/menus/Veget...)