I bought this:
I got it from
www.coolputer.fi/
under the modding section there are 4 items called 'Speedlimit' for 2 or 4 fans. The Speedlimit 4 (LOPPU) is a kit with all components and a PCB for you to solder together (thats the one I bought). The non-LOPPU version is pre-built and costs twice as much.
They do world wide shipping.
What I like about it is that on Booting the pc, the fans run on full voltage for a couple of seconds, then throttle back to whatever setting you have on the Pots. You can also fine-tune the pots so that they wont dial down below a minimum voltage.
I currently run the following config:
POT 1: CPU Fan Coolermaster HHC-001 - 7000RPM Max (rpm monitoring still attatched to MOBO)
POT 2: 120mm fan on side panel
POT 3: 2X 80mm intake fans
POT 4: 2x 80mm outtake fans
FuRy