Any fan that has at least three pins can be controlled via voltage. The Corsair Air series is a fairly solid brand, and I have no issue recommending them for a case fine. Sadly, I haven't read a lot about the AF variant, or own one, to really have much input, but I can tell you that the main complaint about the SP variant is the noise. It's not screaming-like-a-banshee-loud, and actually the type of noise it makes is fairly pleasant, but it is noticeable and I can see it getting on a lot of people's nerves.
I can also tell you that one reason why you don't hear/read a lot of reviews about the AF variant is that people look at the CFM and Static Pressure numbers, and wonder why anyone would buy the AF variant since the the SP looks better on paper. Their reasoning might be justified at full tilt, but once you dial down the RPM...
Anyway! Cougar fans are also pretty good. Their PWM variants often have crappy circuits which will emit a higher pitched noise that overrides the fan, but, with voltage control, you can bypass that.