Seems like one must for an out of towner is Threadgill's. The new one on Riverside and South Congress got a better review for food (in the Chron or the Xcelent the other day-forget which) but the old one on Lamar and 60th or so has great Austin ambience. And, IMHO, the Salt Lick is just great for barbecue; the 30- 40 minute car ride to it through nothin'-exciting-but-typical-Central-Texas makes it seem more like an adventure.
Austin, TX