If you're in dire need of some way to cool down your laptop and don't want to spend the cash on a cooling pad, Instructables has a simple solution in the form of some overturned egg cartons.
Flip some empty cartons over and you get plenty of airflow. Plus you won't burn your legs if you want to actually put your laptop on your lap. It's by no means the prettiest thing, but it's cheap, and gets the job done. An ugly setup is better than an overheating machine.
Cheap Way to Cool Down Your Laptop [Instructables]