Thermalright SLK-800 + Any 80mm fan
I have one running with a Silent YS-Tech 80mm (20dBa, 27CFM) and it cools my XP1800 amazingly.
As far as a lot of people and websites are conserned, its the best air cooled HS out. Cheaper than the Alpha as well, and you dont have to mess around with motherboard holes to fit it.