The Prolimatech Megahalems is the easiest I have ever used.
The ones I am currently using are:
$80 category Thermalright Silver Arrow or Phanteks PH-TC14PE Cooler
$50 Category Hyper 612 PWM or Scythe Mugen 3 ..... about 3C hotter than the $80 ones
$30 Hyper 212 about 5C hotter than the $50 ones