Do you know by now, that you’re going to book a hotel where your going? You might as well book it now then.
By booking your flight and hotel with the same company like Expedia, you’ll be getting a combined discount. You can even add a car rental and save even more, if you know you need it already.
If you don’t fancy a hotel with your cheap flight tickets, consider searching portals like AirBnB and Wimdu for private apartments and houses. AirBnB is an option in most major European cities, Berlin excluded.