I have a spare fan speed controller to sell. I decided to offer it here before putting it on Trade Me.
It's a 4-channel blue LED, 4-pin fan plug controller. It's 3½ inch size. The specs are:
Voltage: DC 5.5 - 12.7V
It's black plastic, very lightweight, with plastic knobs (they don't look half bad though).
Note that it doesn't turn them right off, but for my fans it brings them to almost complete silence (just a slight spinning).
The price is $20 + $2.40 postage (or $3 for next-working-day delivery). Includes fan controller & 4 screws, in box.
See the photo below for it running in my computer.