Cougar Vortex
Noise Blockers
Noctua of course
Be Quiet!
There's plenty of quiet fans to be had and a varying price range. Me personslly, I have 5x 140mm BQ! Silent Wings 2 PWM fans in my Fractal R6 case and it's dead silent. They were like $14 each.
Unironically Noctua. See old fan roundups at Silentpcreview for sound samples.
I run almost all COUGAR CF-V12H
one in front of case sucking in and blowing over HDD racks the another one sucks from racks and blows on graphics cards, one as the exhaust and five on the 3x120x2 radiator I have mounted on the back of my case in a push pull config (except for the middle its just pull because of mount).
very quiet, pretty much the same level as my water pump. even when cranked up all the way, all you really hear is the air moving. I have em all run through a bay mounted fan controller and mostly leave them on low unless I am maxing out the system.
I also have two 140mm fans sucking through the 2x140x1 radiator at the bottom of my case, they are enermax vegas fans with a bunch of preset LED patterns and to jazz it up, they have their own rheostats and toggle buttons for the LED light settings. they look cool but are not as quiet, I leave them on medium as tests have shown marginal decrease in temps at high for a big increase in noise.
Silent Wings 3 are the quietest fans you can buy.
SilentiumPC Zephyr PWM 120
>14 dba max
>48 cfm
>hydraulic bearing system
SilentiumPC Mistral 140
>18 dba max
>61 cfm
>fluid dynamic bearing
Best Value Fans you can get on the market right now if you're on a budget. They typically go for around 5-7$.