Donn's BBQ is in Southwest Austin, 10 min from the airport. You could make it your first stop in Austin, or your last stop before flying home. It is actually good enough to do both!

A nondescript cement block building hides wonderful Q inside.

I ordered up the "Texas plate" (I was a little hungry) which came with Moist brisket, Lean brisket, Sausage.

I was in a bit of a hurry as my flight was in an hour, but I ate most of it. Even went back for more tater salad because it again is very close to my recipe. I managed to eat it all except I again left some beans and a few bits of the lean brisket. Item by item descriptions:
Moist brisket - Nice texture, great flavor
Lean brisket - I have decided that lean is just not my cup of tea
Sausage - Amazing, really nice. They said they get it from V&V whoever that is.
Tater Salad - Nice crunchybits of onion/celery, touch of horseradish, touch of sour cream. Was definitely tasty.
Beans - Nice flavor with little pencil eraser sized chunks of meat floating in it.

I did not order the smoked catfish, but there a couple of guys in the corner table just raving about it. Will have to try that next time.