New link: http://www.ihg.com/coinks
Book 2 consecutive nights at an IHG hotel (Holiday Inn, Holiday Inn Express, Crown Plaza, Hotel Indigo) and get the second night free.
The discount price per night is shown in the results of a search (ie. it's half price per night). Prices are per room, per night including breakfast.
Hint: Keep your dates flexible to find a real bargain - expect to pay as little as £34.50 per room, per night for a city centre Holiday Inn Express.