It all depends on the price you want to spend. Like Jimmy, the Hyper 212+ is a good budget heatsink for only 30$. It's not the best, but certainly one of the best budget ones.
The Thermalright Silver Arrow or Cogage arrow for that matter is one of the, and probably is, the best possible air hsf you can get right now. However it is one of the largest as well.
The Megahalems ubrales said is actually a great heatsink as well, but I would just go with the Silver Arrow, of course both are good hsf.