Cantino

). for 25€ you get a all-you-can-eat style menu (served at your table, no buffet) which is nothing less than delicious. every course includes 6 different tapas (meat, fish, vegetarian - 2 each), which keep on coming until you tell the maître to stop. remember to leave some space for the fantastic desserts-course.
as the restaurant is located on top floor of the Haus der Musik there is a lovely view over Viennas rooftops as well.