A few big, slower (> 1000rpm) 140mm fans will generally be quieter than 120mm fans moving the same air. Since you don't really care about static pressure with case fans, go with the quiet fans that can move the most air. This link
may be valuable to you; the same site also has 120mm-only and 140mm-only fan round-ups as well. The top fans moving the most air quietly are Noiseblocker multiframe and blacksilent fans, Scythe Gentle Typhoons and S-Flex fans, and the Thermalright TR-FDB.
The conclusion page has some good info.
Originally Posted by Siegfried262
I wouldn't recommend using the side fan as an exhaust though, people typically benefit from the fresh air it brings into the graphics card/motherboard area.
I suspect this depends on what kind of cooler your GPU has. On a card with a Twin Frozr cooler, for example, it vents most of the hot air out of the sides between the card and cooler; an intake would only be helpful if it was below the card's cooler so it can suck air upward, otherwise it would only push the heated air back to the card.Edited by BBEG - 8/5/11 at 7:08pm