Well, look up Sharkoon. They make very quiet, yet efficent fans that may get you started
Let me find the CustomPC magazine on case fans, and I'll check what came out at best for you.
Right, the best 80mm fan came out at the Sharkoon Silent Eagle 2000.
It runs at 2000 RPM, yet keeps noise down to 21.5DB and moves 26cfm of air. Alot for a efficent 80rpm fan.
The best 120mm fan was the Sharkoon Silent Eagle 1000. Quiet, and yet, capable of moving 38cfm at 19db (Lower than most noise ambient levels)
They have brought out a 2000RPM model of the 120mm series though which moves even more air. They say 76cfm at 36DB (Not exactly loud)
Silent Eagles have the best noise vs performance, so may be worth looking into.
If you really aren't bothered about noise... then why not get Vantec Tornado's? Haha.... The TD9238H 80MM modwel for example can move 121cfm, yet at 54db, would be overheard...and not just slightly either.