One of the world's largest hotel companies, InterContinental Hotels Group offers a 5th night free deal in most of its properties in Europe, including hotels in Rome, Berlin, Budapest and Madrid.
Booking for hotel rooms in September 2010 will allow you to get every 5th night free. Thus, if you stay for 15 nights, for example, three of them will be knocked off your bill.
The program "Summer Package" also includes a € 100 deposit voucher to pay for food and beverages.