During my last trip to Berlin I stayed at BaxPax Hostel, that I can highly recommend to you. It is centrally located, clean, inexpensive, with good atmosphere. But that is also probably true for many other hostels in Berlin. What makes this one stand out from the crowd is that each single room there is painted in different style.
E.g. the room I stayed in had Miro-like paintings on the walls:
Whereas the corridor leading to my room, was full of tele-geometric figures: