I suggest you edit your thread title (yes, it's possible on this forum) to either nondescript or stealth fan controller.
I'm also a fan of linear fan controllers like the Sunbeam Rheobus (I think jab-tech.com still has the best price when ordered along with other stuff (suggestion: J-T carries some very nice tools

) - if ordered alone, shipping will be excessive) or the Vantec units. The Sunbeam has garish LEDs but those can be muted in several ways including the method JPas above used or you can replace them with lower brigtness LEDs or you can add resistance to dim them or you can simply unplug them as they are mounted in machine pin sockets. The Vantecs have lit rings around the knobs - don't know how easily those lights can be disabled. The Sunbeam has 4 channels while the Vantecs seem to have 3 fan channels and a CCF control.
The Silverstone FP33-B/S (blk/slvr) controller has three channels and has no lights at all and can even be mounted in a PCI slot plate (comes with both a 3.5" bay panel and a PCI slot plate) for the ultimate stealth. The controller circuitry itself is located on a small PCB that can be stuck anywhere in your case that's convenient. It seems to be a PWM (Pulse Width Modulated - aka digital) controller as the pots at the knobs are too small for a strictly passive controller and the PCB isn't big enough for linear, but nothing I've seen is explicit on that nor what power of fans can be controlled. The other controllers mentioned can handle 18 or 20 Watts per fan. I suppose it could be totally passive, but to do that properly it would have to be tuned to the different powers of fans. I don't know how they could spec a 5V to 12V control range and still be passive... If anyone knows for sure, let us know.
Use the price search engines to find your best bottom-line price from a reliable reseller.
.bh.