Club Carlson has an interesting offer for the Europe, Middle East & Africa. When you book for 3 nights using promotion code NIGHT3FR and pay using American Express card, you will get a 3rd night free and 2000 bonus Club Carlson points. This promotion is only valid at Radisson & Radisson Blu hotels from July 15th to September 30th, 2012.
This promotion code seems to work just fine. I was searching for a hotel in Helsinki using the NIGHT3FR. Unfortunately none of the hotels in Helsinki proper are apparently participating. The only Radisson Blu hotel, where this rate is valid, is actually located in Espoo. It did, however, lower the rate from 150 euros per night to an average rate for 100 euros per night by giving the third night free.
You should always check the other rates such as advance purchase, friends & family, and Gold/Concierge offer of 4 for 2 offers as well, before making the final decision. 2000 Club Carlson bonus points is a nice little extra, but not worth a lot.