Currently, my signature PC sits in a cabinet, and unfortunately, it doesn't have much in the way of ventilation at the back. Now that it's coming up to summer here in Australia, it was really starting to warm up in there. Parts of the case (especially near the GPU) were getting way too hot for my liking. The solution? 

The fan i used (an Acrtic Cooling Breeze USB Fan) has a stiff stand, but it wasn't stiff enough to hold it in place, so I used some sticky tape around the stand and the thumb screw on the case.

"Installed" on the side panel

Perfect! Now it blows air out the cable hole
It works well. The case only feels warm now. It doesn't get anywhere near as hot as it used to.

The fan i used (an Acrtic Cooling Breeze USB Fan) has a stiff stand, but it wasn't stiff enough to hold it in place, so I used some sticky tape around the stand and the thumb screw on the case.
"Installed" on the side panel
Perfect! Now it blows air out the cable hole
It works well. The case only feels warm now. It doesn't get anywhere near as hot as it used to.