Like dylanvdang001 said, Be Quiet! fans are also quite good. They're slightly quieter than Cougars, and real-world performance is about on par, although I think at full tilt the nod goes to Cougars. The only downside is that they can be difficult to find, and are expensive. I think NCIX has them regularly, and amazon gets in a shipment every couple months.
Beyond that, Enermax and Arctic Cooling make good, affordable fans that you really can't go wrong with.
Corsair SP120 Performance editions are great for absolute performance, but can be a bit on the loud side. (Not overly so, but noticeably so.)
A lot of people recommend Noctua fans. I personally haven't tried them yet because they are expensive; I have not justified purchasing one for myself quite yet.