Yeah heat and laptops are really bad. If I'm on my laptop any extended time I use my laptop cooler. Basically its fans that are under the laptops that blow cool air on them.

I have a 17" laptop so this is the one I use and it really does move the air:

VANTEC 17" Aluminum LapCool Pro Notebook Cooler Model LPC-P100

At the very least prop it up so it can get more air under it. You can see more coolers here at Newegg. They also sell them at and office supply store (like Office Depot, office max, staples...Best Buy).

Also when its not in use shut it down - not asleep but shut down.

addon: a cheap way to prop it up is put it on top of a wire cookie sheet cooler

They make laptop cooling fan accessories that sit underneath laptops / notebooks, that plug into a USB port: Like These

That might be enough to take care of the problem, but if it's something new happening, you might want to see if you can track down what's causing it before something bad potentially happens, like hard drive failure and data loss. Some possible causes could be a hard drive going bad (bearings or other friction), video card overheating, regular internal fan(s) malfunctioning, etc.

Edit: Oops, SM beat me to the punch. Woot!

my boyfriend uses this targus one http://www.officedepot.com/a/products/587815/Targus-Notebook-Chill-Mat/

Ohhhhhh look what is on sale Black Friday: Clicky