Noctua NF-F12's, Silverstone Air Penetrators and Scythe Gentle Typhoons 1850's are the typically recommended radiator fans, their pretty good.
Though what fan to get depends on your radiator. If your talking a slim low FPI rad, you really dont need anything special in terms of fans. Get yourself a High FPI 80mm thick rad, you better get good fans or you will get nowhere near its potential performance.