check SilenX's products, best airflow/noise ratio that I've seen. they do seem to be a little louder than thier ratings, but they are still extremely quiet.
iirc there is a company that makes a silent heat pipe/heatsink alternative for GPUs, getting rid of a fan on the GPU all together.
In my experience, component loudness is usually attributed from virbration. eliminate vibration and lot of the sound will go away. Tricks include rubber bands on hard drives, rubber grommets around screws, zip ties, cutting fan grills for less restrictive ones, using better thermal paste, push/pull fan setup, etc.
if you have your fans hooked up to the motherboard, then try a program called Speedfan, you can adjust the fan speed within windows. it also delivers temperature and voltages.
A few(lots) words on loudness/CFM:
dBa/db is decibels, this is a measure of sound.
for each 3 dbs the LOUDNESS of the sound DOUBLES. for example: fan of 13db is 4 TIMES as quiet as a 19db fan. Some manufacturers don't have "correct" db values,
more CFM means more airflow, but airflow is nothing if you don't have pressure. This is also where loudness comes in, turbulance, which makes noise (kinda). If you've ever been to a large, open area such as a football(american or the rest of the world) field or a beach, you know that wind isn't exactly "quiet", it bangs up against things and creates that "woosh" sound. This is part of what you hear from fans.
now, back to pressure. If your fan has lots of CFM and not much static pressure this basically means that it will move lots of air, but not "through" things. for large watercooling/radiator/heatsink applications you want something with lots of pressure to push/pull air though the heat source. This is why it is good to remove grills, less for the fan to push air though, and more area for it to push it through.
Many people to get lower temperatures with less noise they run two fans, in tandem, sometimes at different speeds, one pushing air, and another pulling air. sometimes they will make an adaptor for the standard 80mm size to a 120mm fan, which usually pulls the air from the regular, 80mm fan on the other side of the heatsource or fan grill.
lowering temperatures esentially lowers the need for fans.
there are many ways to go about doing this: better heatsink design, as mentioned, Zalman makes great products, extremely large and heavy though, most are made out of copper, sometimes aluminum since its lighter, but not as good to conduct/release heat.
An easy way is to get some nice thermal compound or thermal paste. look for the expensive stuff that has silver in it.
Another way, more extreme and sacreficing slight speed is to "underclock" the processor and graphics card. I'm sure you've heard of overclocking, to get MORE speed out of something, but this is just the opposite, lower speeds and lower voltage to use less power and in turn, produce less heat. This means you don't need to use an overpowered/loud fan.
I guess thats about it, I hope I didn't lose you in any of that, I know it was a lot, my fingers are tired
Good luck!
-Jackson
