If you are traveling on a budget, Walden is the place to go! It's situated next to the famous Dom tower and it is a famous place among students. You can get a lunch deal for €6 including a (non-alcoholic) drink and for dinner they serve a 3-course menu's for only 15 euro's. They also have a nice variety of beers, so also for just a drink.
They also have a dj playing from time to time.