This is the place to go to when you need to have something fast and cheap but filling. This italian restaurant has a pizza counter where you can get huge pizzas or just slices (which are big enough if you need a quick lunch or dinner!), and in the back there is a self serve restaurant section with excellent italian and local dishes. There are about 8-10 types of pasta (bolognese, arabbiata, etc, the usual italian pasta dishes), veggie and meat lasagne, some yummy casseroles, a few meat dishes (chicken skewers, wiener schnitzel, etc) and a soup of the day (mostly local soups). The staff is friendly and the servings are HUGE!
Bizi is a restaurant chain, the location I frequent is at the beginning of Mariahilfer Strasse (see address above), but I know there is another one behind the Stephanskirche (if you walk to the church on Kartner strasse, pass the church and continue ahead on the street that continues the line of the Kartner strasse and you will see the sign on the next corner).