What is your budget?
Best bang for your buck would have to be the Hyper 212+.It's fairly cheap and provides really good temps.Their are lots of people who use the 2500k and the Hyper212+ and O.C. to 4.5ghz and above.Remember it all depends on what type of chip you get for how far you can "safely" O.C.
Hyper 212+ Evohttp://www.newegg.com/Product/Product.aspx?Item=N82E16835103099
But if you do have more money then I would suggest going with something from Noctua.
Here's a list that might help you.http://www.frostytech.com/top5heatsinks.cfm