Noctua NF-A12x25 5V, Premium Quiet Fan with USB Power Adaptor Cable, 3-Pin, 5V Version (120mm, Brown)

Pros: One of these fans mounted on my NH-U12S matches the performance of TWO NF-F12's mounted on the same cooler.
At max speed (2000rpm) this fan is objectively quieter than a NF-F12 at it's max speed of 1500 rpm.
Comes with all the Noctua accessories in the box, including a cool gasket for creating a better seal when mounting to a radiator.

Cons: Only available in the standard Noctua colors, and only available in 120mm so far.

Overall Review: I'll try to keep this short. I replaced a NH-D15S with a single fan, with a NH-U12S running one of these, and I've noticed hardly any difference in temps/noise. That's incredible.
After I swapped the coolers/fans I ran the Asus Fan Suite tuning utility, and I was expecting to hear the fan roar as it ramped up to full speed, but I didn't notice any noise really... So I went into the fan control software and manually set the fan to max speed and I was awestruck by how quiet it is. For reference, I've also got a NF-F12 and two NF-A14's in the same case, all PWM controlled. This fan, at 2000rpm, it noticeably quieter than the other fans at 1500 rpm. I really don't even mind the Noctua brown color scheme, the performance is so impressive.

Pros: >Amazingly quiet for 2000rpm fan. At max rpm as loud as a normal fan at like 1300rpm
>very strong static pressure. You can feel the force. No issues blasting through a heatsink at all.
>the gasket it comes with isn’t the thickest but it’s awesome noctua includes one at all. even though it’s not the thickest it still helps reduce vibration and prevent scratches.

Cons: I own a total of two with both purchased months after each other, and both have issues. The one fan rattles pretty bad. If I pick it up and just very gently move it, the fan assembly moves. That’s how bad it is, and both have issues of “seizing” up. Both have the chance of doing it with a reboot and the one just randomly seizes up (stops moving) even when in use. If I try to move it manually I can’t. It’s like the motor just locks up. Just to note I’ve been very gently with them. I never threw them, tossed them, banged them against anything. Nothing like that at all.

Overall Review: I’ve been meaning to contact noctua about it but honestly I’ve been busy with work and moving 1500 miles across the country. Twice. I just haven’t gotten time to. And I’ve also lost their boxes in the move and most of their accessories. I really like noctua and when these fans function normally their amazing. Hands down the best performing fans on the market. But just beware, not all are perfect.