well from what i hear, the cooler for the xbox 360 actually makes it over heat more because it uses more power, thus making it over heat more.... so yea don't get one...
Your best bet is the Nyko Xbox 360 Intercooler. It plugs directly into your Xbox and uses the power already generated for the game so no extra energy is being used. It just makes your Xbox 360 a little cooler and more energy efficient.