I can recommend:
Cafe Hofgarten.
In the (where else?) Hofgarten across from the Congress Zentrum. Like a beer garden, great outdoor ambience, surprisingly good food that we will visit again. My husband's colleagues who work at the university recommended it. Soups, salad, traditional Austrian grill items. Great place to unwind after a day of work (for hubby).
Thai Li
Old town. Wonderful break from heavy Austrian food.
Löwenhaus
North-ish of old town along the river. Nice beer garden, surprisingly good fish dishes.
Goldener Adler
An outdoor restaurant in the pedestrian area of old town. Good traditional Austrian food with great people watching.
Food Hall
On the river in the old town. Bought food for the train trip here. Can't remember the German name.
The restaurants above are inexpensive, not cheap. They also have varying degrees of tourists. But they are good and fulfilled my need for German (well, almost) cuisine from my days of living in Germany.