Make a passive (air) cooling laptop stand. The basic principle is simply getting the laptop up off the ground (or off your lap) to facilitate natural air flow beneath the laptop. Many sell for ~$30 like the one shown in the images (and may be worth the money) but while you're deciding whether to buy one, why not make one yourself?
Step 1: Gather The Goods
Here's a picture of everything you'll need. Things not shown in the picture you might need: Sharpie and a cutting board (in the picture, just forgot to label it). I happened to have an obscene amount of dry-cleaner's clothes hangers, so that's what I decided to make it out of. Go figure. :P