If you are serious about building a high end gaming PC, then you should either go for Corsair Vengeance DDR3 RAM or Kingston HyperX DDR3 RAM.
Corsair Vengeance DDR3 RAM:
This RAM comes with a great memory clock of 200 MHz and comes with an effective frequency of 1666 MHz. Hence, it will give you a huge leap in performance. Moreover, I also have this RAM and to my wonder it can easily handle heavy video editing and does not hang the system while jumping from one scene of an HD movie to another. And on Windows 7, this RAM shows a rating of 7.5/7.9. Earlier, my rating was only 5.2/7.9.
Kingston HyperX DDR3 RAM:
This one is even better than the Corsair Vengeance RAM in my opinion. Kingston HyperX RAM comes with an incredible memory clock of 667 MHz which comes with an effective frequency of 1666 MHz. So, if you buy this one, then I assure you that you will never regret your decision.
I personally suggest you to buy Kingston HyperX RAM as it provides better performance than the Corsair Vengeance.
PS: Corsair Vengeance is a way better at heat dissipation than the Kingston HyperX one. So, choose wisely which will suit your system better.