Fan controler is a must / or use intergrated hardware profiles (abit uguru etc)
Aim for a case with minimal holes and vents and a simple air path
Door on the front is also good (but that limits fan controlers)
The Accelero S1 run passive is excelent with a good airflow and most cards.
As ever it's what in side that makes the noise / heat so select hardward accordingly.
DO YOU REALLY NEED A QUAD? movies=no, games=no, web=no, photo's=no, CAD=maybe, render/encoding=yes
Select a performance level and get the lowerest power draw / heat generated hardware in that band.
Isolate everything - bungee/rubber arrowheads/gromits etc.
If the case is tidy and cool - two or three fans (total) will cool it very quietly.
My
[email protected]@1.1v in a LL S80B is currently running on air - single noiseblocker S2 intake - stock cooler (low rpm) - fanless psu - passive 8800gs (600/1880/900)
It's not dead of night silent - but just above ambient during the day.
GS runs at 51c load 41c idle (folding@home) less in games, CPU is an ES so no core temp for me

says 38c in bios idle