Almost all of today's desktop CPUs (with the only exception being VIA's C3) require a fan attached to a heatsink to keep them sufficiently cooled. When choosing a fan to go with your heatsink, there are a few important things you should look at. The first is the type of fan.
Two types of fans that usually come with heatsinks are ball bearing fans and sleeve bearing fans. Most people prefer ball bearing fans rather than sleeve bearing fans because they spin faster, thus increasing cooling performance. Sleeve bearing fans have also been known to fail when they get old, which would be a disaster, especially for owners of AMD processors, since seconds after the fan stops working , the processor will be fried. A good way to tell if your fan is of good quality is to carefully listen to the sound if makes while it's running. you should just hear the sound of the air flowing, which can sometimes be rather loud depending on the speed of your fan. You should not hear a buzzing sound and if you do, chances are your fan's motor is poor.
If you would like high performance and do not mind a high noise level, I recommend a 7,000RPM ball bearing fan. However, if you would like a relatively quiet PC, you should be looking at a fan that rotates at around 4,000RPM.
Thermal Interface Material
To have the best possible heat transfer, the base of your heatsink has to be flat and free of air gaps. While a heatsink's base may often seem flat, there are always tiny bumps and dents that you cannot see and no matter how much you lap your heatsink, you will never get it perfectly flat.
To combat this problem, a TIM (Thermal Interface Material), such as a thermal compound or thermal pad, is used. A thermal pad usually comes preinstalled on a heatsink and is made out of graphite or some sort of polymer. while no installation is required and they are all that is need for most users, the performance they offer is far inferior to that of a thermal compound.
A thermal compound is a paste that is applied to the CPU or the heatsink. Most thermal compounds consist of silicon, silver and metal oxide. This is because these materials provide especially high thermal conductivity.