Without question one of the most affordable and thus commonly upgraded components by PC builders and enthusiasts alike is the CPU cooler. While things have definitely improved in the past few years, upgrading the stock cooler that comes with AMD or Intel processors still grant you a number of improvements. Generally the main goal is to lower operating temperatures, but aftermarket coolers can also reduce operating volumes and provide a greater overclocking headroom.
Included in the comparison are the Thermalright True Spirit 140, Prolimatech Panther, Thermaltake Frio Advanced and Noctua NH-C14. All four are designed to support multiple platforms on both AMD and Intel camps. They range in price from just $40 all the way to $85, so it will be interesting to see how they compare and more importantly what they offer over stock cooling units.