The stock fan is alright if you don't want to overclock. If you haven't installed it yet, remove the thermal pase that comes pre applied and put some on yourself, after watching logan's thermal paste video.
The stock fan should perform decently in most applications as long as you're running the CPU at stock speeds, but if you're running more demanding applications (things like video rendering or 3d modeling) then you're probably going to want to go with a better cooler. I've seen Intel CPUs go over 80C in Prime 95 stress tests with the stock heatsink and fan, which can be dangerous.