Most likely some may have already done this, but I thought I would save some testers time if they are contemplating overclocking and cooling the Raptor with E2.
I use the laptop cooler #8425 from Monoprice ($12.00+) that has a very quiet fan along with four usb slots. It works well when using E2 and overclocking the box to 500. Absolutely no problems to date. Have used it at 600 for a week recently, with no problems and no need to remove the cover.
DISCLAIMER - Overclocking - do so at your own risk.