A few notes:
Crossfire (for AMD) and SLI (for NVIDIA) means that you use 2 GPUs for higher performance.
Intel is currently in the lead as far as gaming CPUs.
Get an HDD with 500 GB+ Space.
I recommend getting an SSD for faster app and OS loading times.
If you choose to have a SSD as your boot drive then the price will go up of course but the performance increase will be worth it. The question is how flexable is your budget. The components listed can be changed of course to help make room for the SSD if that is what you want. The whole thing comes down to what you want to do and what you want to pay and what components you want.