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
Step 2: Getting Started: Crimping
Position two clothes hangers with hooks touching. Straighten each hook using pliers, then begin to wrap the metal around the opposite hanger (I used two pliers, one in each hand to easily bend the metal). They should both be firmly crimped to each other when finished. This step is probably the hardest.
Step 3: Adding Support
WARNING: Do not cut like shown in the pictures. My hands were positioned like that only for the purpose of taking pictures.
Now we'll add the support dowels running perpendicular to the initial set. Cut these new dowels down a bit to match the footprint of your laptop (e.g. my PowerBook is widescreen so i need a rectangle, not a square). Now, on each end of these new dowels, cut a 1" slit. Insert these supports on both sides.
Step 4: Wired Up
WARNING: Do not cut like you see in the pictures. My hand is positioned like that only to take the pictures. Always keep your hands away from the sharp side of the blade.
Cut triangle wedges (indicated in pink) out of each cardboard dowel using a knife. All cuts should be equal distance from each corner (3-4 inches out).
Next, slice open your Cat5 cable to reveal the twisted pairs inside. Choose a color you want (doesn't matter) and unravel the twisted pair. An easy way to do this is to stand up with a wire in each hand (making sure your arms are raised enough for the cable to be off the ground). Then, slowly pull the wires apart. It will twirl around while separating at the top. If you pull too fast it will tangle up. No Fun.
Step 5: Cinch the Corners
Wrap the wire around all the corners, using the triangle wedges you cut out earlier, then with pliers, twirl the ends together to pick up the slack and make it taught. This should pull the corners together.
Step 6: Quick Fix
Uh oh. It looks like we got a little problem. The side beams might start to bend from the tension from the wires. We'll insert some support beams in the middle to press the sides out again.
Run a wire from the Cat5 inside the center support dowels, loop it around the side dowels (indicated in blue), run it back through the middle support dowel, then tie it off around the wire hangers in the middle (indicated in blue). You can then twist the wires with pliers to finish off.
Step 7: Laptop Supports
Now we'll add the supports the laptop will actually sit atop of.
Get two more full length dowels. Poke a hole all the way through 2 inches from each end. Now, either using stiff clothes-hanger wire, or Cat5 wire, secure this support running parallel lengthwise. These should be closer together so your laptop can sit nicely on them.
Step 8: Gription
Add the rubber grips to help the laptop stay put if the stand is at an angle. Cut a dowels to fit perpendicularly between the laptop rests. Place the rubber shoulder grips (that come on some clothes hangers) around the dowels, then secure the dowels using wire, running it through the middle, wrapping it around, then tying it off like before (indicated in blue).
Step 9: Padding
Stretch the foam padding across the dowels. This will prevent the laptop from getting scratched from any and all of this wire that could touch it.
Step 10: Finished!
Well, that's it. This is a cheap and industrious way to cool your laptop down if you're tired of it burning your legs or just cool down while doing processor-intensive tasks.