There are lots of case fans that provide quiet cooling, too many to list really - All you need to know is find the best combination of air movement vs noise vs cost.
www.quietpc.com has some good info on each of the fans out there =)
As for how many you need, well that depends on how hot your system is getting. A typical setup would normally have at least 2 case fans, one in the front, one at the back. Given your GPU, I would say 4 would be better.
1 at the front, 1 at the back, 1 at the side(if possible) and 1 at the top (if possible). Depending on your environment, I find negative pressure works best, so have the front sucking in air, all the others push out - but this is my personal opinion here hehe =)
Hope this helps