Sorry , Forgot to mention.
I have considered this GPU and I wil be installing only one unit of it : 'AMD/ATI Radeon HD 6670 1 GB DDR3' GPU. I think it would suffice for now and it has also got some good reviews too.
Please also consider Corsair and cooler master brands also for the PSU.
Thanks to dear friends:
Rugger , Rolli59 and blade061188.