Any cooler that supports LGA 2011 will fit. The socket was designed such that it should be compatible with most LGA 1155 and 1366 coolers as well.
The Sandybridge-E processors are massive power hogs though so you will want a good cooler. A custom water cooling loop would be ideal but the Corsair H100 works well. I haven't tested any air coolers on it but I'm sure there are a few reasonable ones.