Nyko just introduced (via ExtremeTech) the intercooler 360 accessory aiming at keeping your Xbox 360 cool.

Game accessory Pelican has since a while already the Xbox 360 fan stand on the market.
Both Xbox 360 accessories sell for $19.99. The Nyko Xbox 360 Intercooler looks more high-tech though. It snaps-on to the back of the Xbox 360 console and is powered through a power cable pass-through. Nyko says it reduces temperature by 2-10 degrees Fahrenheit.
Amazon sells the Nyko Xbox 360 Intercooler for $19.99.
The Pelican PL-3619 fan stand offers besides a fan also a save stand for putting the Xbox 360 up-right. It has though an extra power-button, which means you have to switch-on and off manually.
Amazon.com sells the Xbox 360 Swivel Stand for $19.99.