TomDuncan :
8GB (2x 4GB) DDR3 SODIMM (204 pin) RAM what is the best priced and the best performance
I don't know where you're from and can't tell you that one specific model is better than the other, but you want at least 1600MHz with cas9 or 8 when you start going up with the frequency you will see that the latency also increases, meaning that performance will be pretty much the exact same...
So just look for the cheapest DDR3 RAM you can find with 1600MHz or more and decent timings ;D
Also I might be shallow, but I always see if the RAM will look good with my case, mobo and other components!