However, I had a dead dual-fan desktop power supply laying around as well as a fan I tore out of a different power supply (replaced it with a blue fan).
I also had another old PSU lying around that I replaced when I upgraded my graphics card. So, with all of these, I built a very effective laptop cooling fan.
Step 1: Do You Need to Cool?
Use PC Wizard (www.cpuid.com) to inspect the temperature of your CPU, motherboard, and GPU as you play games (I hooked up a second monitor, put PC Wizard on it, then fired up games and watched the temperatures change). You can minimize PC Wizard and it will have a small status/temperature notification at the top right of your screen.
Step 2: Take Apart the PSU!
Computer power supplies (PSU's) have capacitors that can carry a powerful shock, enough to kill you. They hold this charge for a fairly long period of time. If you take apart a PSU, you're safe as long as you don't touch the underside of the circuit board OR any of the capacitors OR any of the metal contacts on the parts...in general, just don't touch the metal stuff on the circuit board. I touched the heatsinks, but those are usually just grounded so no big deal. Wear plastic gloves if you so desire. This PSU was a $13 model purchased from Newegg to power a cheap rebuilt PC. It lasted 3 months before I accidentally bumped into the PC and the flimsy heatsinks touched and shorted and fried the PSU (not the computer, thankfully) and took out my whole room in the process (stupid GFI). Newegg RMA'd it and sent me a new one, but due to the cheapness of the PSU, didn't ask for the old one to be returned. Instead of just throwing it out, I figured I'd salvage stuff from it. The first thing to take are the fans.
Take apart the PSU by removing the cover screws. Then you can take the fan off by unscrewing the four fan screws (usually from inside the PSU case). Repeat for the rear fan if your PSU has one.
If you don't have a dead PSU, you can buy cheap case fans online, buy expensive case fans in stores, or ask people who have lots of computers (they might not give them to you though...). You can also find a dead PSU from said people.