[VIDEO]http://www.amazon.com/gp/product/B0016CMCBG/ref=ox_sc_act_title_1?ie=UTF8&m=A2XNAOBSW0CZDL]Amazon.com: Scythe mini-KAZE ULTRA SY124020L - Chipset fan - 40 mm: Electronics[/VIDEO]
...Unless someone has any cooler (ha) options. There *is* a 40mm fan with LED's...
[VIDEO]http://www.amazon.com/Crystal-40x40x20mm-Clear-Blue-DF0402012BBH3A/dp/B001BLNE32/ref=sr_1_21?ie=UTF8&qid=1311963765&sr=8-21]Amazon.com: Crystal 40x40x20mm Clear Fan with 3 Blue LEDs DF0402012BBH3A: Electronics[/VIDEO]
...And while it pushes twice the air, it's also twice as loud. Still researching...
I have one of these behind my iMac that I use when I'm doing long transcodes (90%+ CPU usage for a long time = teh hotness):
[VIDEO]http://www.amazon.com/Optimus-High-Velocity-Fan-Diameter-F-4040/dp/B001IYQPWO]Amazon.com: Optimus High-Velocity Fan - 4in. Diameter, 35 CFM, Model# F-4040: Home Improvement[/VIDEO]
It was like six bucks at Wal-Mart and is quiet as hell. I'm going to get a second to slap into my rack. Thing is awesome.