One thing you need to know about Austin eating - everything is bigger than anywhere else. In Texas, size matters... at least when it comes to food and Austin is no different. Austin offers a great diversity of food from Japanese through to your finest wheat germ. As you can imagine, there is plenty of Tex-Mex and Mexican food. So, some of Austin's best:
Guero's. This is the only place in Austin for Mexican food and fish tacos. It's on South Congress, which in my opinion is the most fun street in Austin. Stay at either the Austin Motel or San Jose and this will be your local. For once, portions are a reasonable size and the quality is excellent. It's a pretty informal place and heaves in the evenings so be advised to arrive early.
Stubb's (Red River). This is Austin's most famous barbeque (or BBQ) joint. It's big and quite a tourist attraction but the food is good. Resist the pulled pork at your peril. They also host great live music many evenings and mostly artists of international acclaim. Grab a cookbook when you leave - you'll never use it but it will gather dust well.
Threadgills (W Riverside Dr). It is not as good as it's apparent glory days but grab a slice of Austin heritage here. Janis Joplin played there before she hit mega-stardom. Music nowadays unless a known act can be hit and miss. Give the chicken fried steak a go - it's not the best in Austin but quite fun. And no, it's not 2 meats as I thought - it's steak battered like fried chicken... much to my disappointment.
Speaking of Chicken Fried Steak - pretty good effort was in the Austin Land and Cattle Co. (N Lamar & West 12th). They do a decent steak there too.
Magnolia Cafe (S Congress). If you want to eat any hour of the day go to Magnolia as they are open 24/7. Food is simple and fresh and of excellent quality. You can get a good pork chop there. Breakfast is great too - if they have blueberry pancakes, order them. If you're like me and are a weedy Brit, go for 2 rather than 3 regardless of what they tell you because they're huge. You'll be told 'you're in Texas now honey'. Ignore them - you'll be sick (I nearly was).
So... go eat and holler y'all till the locals get rowdy.