If your budget for the graphice card is just $150, then here is a the 3 components. The total cost is $311.65 USD, and it will use an estimated 335watts. Look for a 400w PSU if you don't already have one. PCPartPicker part list / Price breakdown by merchant / Benchmarks
Is there a certain price range? Do you prefer AMD/Nividia/ATI?
There are alot of GPU's that will work, you just need to find one that suits you and doesn't bottleneck. Fore example, a GTX Titan would work, but the raw power of the thing would bottleneck from here to the moon and back.
If your budget for the graphice card is just $150, then here is a the 3 components. The total cost is $311.65 USD, and it will use an estimated 335watts. Look for a 400w PSU if you don't already have one. PCPartPicker part list / Price breakdown by merchant / Benchmarks
then buy the 2gig 6950/7850/7870 and see how it goes. you don't need a motherboard and although the power supply is a little light for me, I think the system will still run okay.............. if not, then worry about spending the extra money. what is your monitor resolution?