I use and recommend the Xigmatek Gaia, which costs a lot less ($22 on Newegg recently) but is superior to the more often parroted Hyper212 EVO:
http://www.techreaction.net/2011/07/07/review-xigmatek-gaia-sd1283/7/
http://www.techreaction.net/2011/11/27/review-cooler-master-hyper-212-plus/4/
Unlike the Hyper212 EVO (ignore the URL; it IS the EVO they tested), the Gaia never throttled, although it wasn't always the coolest depending on the fan used. Both got awards, but if you factor in the price, the Gaia wins hands down.