Fans are a good, cheap way to keep your system cool. They come in many sizes and can be adapted to fit nearly anywhere in a computer system. Generally, the more air flow you have running through your computer the cooler it stays. However, the faster they spin the more noise they make. There are larger fans that spin slower and are quieter. You can get them with lights and in different styles and fin types to fit your needs. If you want a quiet system with less fans, check out the liquid cooling systems.