Well, you have options. Generally speaking a typical 80mm medium speed case fan should do. But typical 80mm fans are noisy. You would be better off with 2 or more slower, quieter fans, if you really want the system quiet.
Also, brand does matter to some extent, especially at higher speeds. Better fans have better bearings and more optimized blade shapes that help reduce noise. I recommend Panaflow fans. For good cooling and low noise, a couple low speed Panaflows would be a good choice, but one might be enough.
Now, the power supply also exaust heat. If you have one with an exhaust fan on the bottom, it will pull heat from the processor. Enermax makes some quite power supplies in this configuration. You might get by with just that, or better yet, one of those and one low speed Panaflow.
<font color=blue>You're posting in a forum with class. It may be third class, but it's still class!</font color=blue>