Well, Noctua fans are universally accepted as pretty much the best of the "quiet" fans. Can't go wrong there. They're fugly as sin though with that maroon-beige color scheme.
Personally, the "quiet" fans I've used are:
Noiseblocker Multiframe and BlackSilentFan series
Enermax T.B. and cluster series
Scythe S-Flex series
Vanteq stealth series
Gelid TX series
Silverstone SUSCOOL series
Of the models I've listed, the ones I would not recommend are the Vanteq ones. Just horrible.
For the others, I've had to volt mod both the Noiseblockers and the Gelid fans to make them quiet to my ears but they were pretty good otherwise. The Silverstone's were good as is, but they have a built in thermistor to speed up and slow the fans so I don't think I've ever heard them at full blast.
My personal favorites of the bunch is the Enermax T.B. fans (and the clusters, but I don't think they make them anymore). They are relatively inexpensive, near silent, and the blades pop-out for easy cleaning. They have a batwing design that they claim helps boost airflow, but I can't verify that. They also come in 3-pin, 4-pin PWM, and LED versions.
I'd do Noctua, the chicken skin and poo brown is a status symbol, right?
That's what I tell myself at least.
They're really quiet and still push a lot of air. I have 7 S12.
I liked Red LED fans so I just got the NZXT sleeved LED kit for my case and it still looks lit.
Best of both worlds.