Interesting video on recycling an old PC CPU/GPU Heatsink to keep a R-Pi cool. Though this uses an R-Pi3 which runs very hot, this can be applied to any R-Pi, especially if you over-clock yours.
 
The problem here is fitting an Old PC CPU/GPU Heatsink to the R-Pi and this guy's solution blocks out the needed ports but otherwise works in keeping the R-Pi3 cool. Very Cool!
 
But something about using a heatsink that is as big as the R-Pi itself.... Hmmm...
 
Enjoy the Video. It is very educational.
https://www.youtube.com/watch?v=1AYGnw6MwFM