Just use a PC cooling fan, anything from 8 Inch to 12 Inch (80 mm -standard size case fan, or the 120mm which would move a lot of air at lower speeds, quietly) Try and get a vantec However they need 12 Volts of DC power because its a PC part
http://www.ncix.com/products/index.php?sku=10795&vpn=SF12025L&manufacture=VANTEC
Cheers

1xAxiom ax 1.2 2xPolk Audio R30 2xMordaunt-Short 3.0 H/K AVR 225 Paradigm PDR-10 Sub HTR MX-500