You can start at http://www.tomshardware.com/reviews/best-gaming-cpu,2545-7.html and begin reading thousands of web pages about CPUs. But you might want to consider the GPU is more important in gameplay.
Here's the link on that -> http://www.tomshardware.com/reviews/best-graphics-card,2569.html
ok i want to know what the difference between intel core i5, intel core i7 and amd phenom 2.
which one of the 3 is better for gaming and why