How can I keep my laptop from overheating?

Keep it on a more flat surface and not your lap if you are.

You could try putting it on some pieces of plastic or wood to keep it off the surface and get it some air. Just don't cover any fans.

• If you don't need maximum graphics and CPU performance, back those down in your System Preferences so the laptop can run a little slower and, as a result, a little cooler.

• Use your laptop in a well-ventilated area and put it on some kind of elevated surface so airflow can circulate under the machine. Don't use it on a bed, flat table top or the floor because that allows excess heat to build up.

I know you said you don't want to use a "cooling pad," but in case you meant active cooling type pads that require batteries and run a fan, there are alternatives. I use a Podium CoolPad which isn't an active "cooling pad", it just elevates the laptop slightly and angles it for better working angle; you can even buy a small travel size that fits easily in a laptop sleeve pocket. On my desk, I use this stand to elevate and allow airflow under & around my MacBook Pro:

dont cover the fans and try to prop it up on something at a small angle like i prop mine up on a book when i sit at my desk so the air flows better.

Buy a laptop stand for it or reset it every two hours

open your laptop and see if there is something in the fan. I mean, clean up your pc or mac...

http://www.youtube.com/watch?v=e30ifz8sxOc <--- what what Chris said

You could try getting a cooling pad. Another way, is to run this great program called "SpeedFan." However it does not work on all computers, but give it a shot, it might work on yours!

EDIT Sorry I didn't read that you didn't want a cooling pad. Just try SpeedFan.

I made a DIY laptop stand with a small 3 ring binder. I cut holes where the fans on my laptop are, it works well for me.