Features To Look For
Fans are fairly simple. Therefore, they don't come with many options. But there are some options worth looking for.
The most important feature is the ability to select the fan's speed. This is often a standard feature, but some budget models don't offer it. It can be tempting to buy those models, since they typically cost only a few bucks, but I would advise against it. The ability to adjust the speed of fan, which usually manifests itself in a switch attached to the fan itself, gives you the ability to calibrate the fan to your personal tastes. If you prefer performance, you can turn it up, but if you prefer silence, you can turn it down.
Taking flexibility a step further, some fans come with connectors that can be fitted into the "fan" slots on your motherboard. These connectors have three or four pins. Three pin connectors will report fan speed to the motherboard, and four-pin connectors allow the fan speed to be controlled from the mobo if the fan supports Pulse Width Modulation. Fans with four-pin connectors are generally the most expensive products, such as Arctic Cooling's PWM models. However, this grants the ability to adjust fan speeds without opening the case, either by using software provided by your motherboard manufacturer or by using a third-party program like SpeedFan . This can result in the best of both worlds - your fans will remain quite at idle, and they'll provide maximum performance under load. Plus, the price difference isn't really an issue: PWM fans are 3-4 times more than a cheap, non-adjustable fan, but that adds up to about six bucks, and the functionality is well worth it. The problem is finding them, as Newegg only stocks four models, including this unit from Scythe. For a wider selection, consider a PC cooling specialist like FrozenCPU.com.
LED lighting isn't useful for reducing noise or increasing cooling, but it is a feature that should be remembered. Some users will prefer the eye-catching quality that a LED fan can bring to nearly any case. On the other hand, fans with LED lighting can be extremely distracting in dark rooms, and are a very poor choice for PCs meant for home theatre use.