In case you arrive in Berlin without having been able to find an apartment before, you should make a reservation in a hostel or hotel in advance:

• Hostelbookers in Berlin
• Hotel Reservation Service
• Hostels and Guesthouses in Berlin
• Youth Hostels in Europe
• Freiraum Berlin
• Hotel-Pension Dahlem (near Freie Universität)
• Visit Berlin
• Short-Term Rent