What's your budget and goal? (overclock? quiet PC?)
You can refer to this thread for some ideas:
AKG? Best Coolers for Sandy Bridge 2500K-2600K OC
I have a Prolimatech Megahalems (1 fan) and I find it overkill for my 2500K overclocked to 4.2 GHz. At full load (F@H SMP) my CPU doesn't go past 50 degrees Celsius even when I turn off my case's top exhaust fans.
If you look at some reviews, you'll see that you can overclock a 2500K even with the stock cooler, but it will be one of the louder fans in your case if you do so.