Digitalmohsin, I have a rule of thumb about cutting edge hardware that can play all of the latest games. The rule is: any system that you build today will continue to be leading edge for about 18 months. At the end of that time, the system won't be obsolete, but it will be possible to build a new system with better parts that will be the *new* leading edge.
To echo what raphoenix says, and add my own input, leading edge parts for today would be:
CPU: Intel Core i7 series
Mobo: Intel X58 chipset
RAM: 6-12 GB of DDR3 1800+ MHz memory in a triple channel configuration
GPU: GeForce GTX200 series, or ATI Radeon HD 4870 X2
HDD: High-speed SSD for OS, 1 or more 10k RPM hard drives w/32 MB cache for storage