What graphics card will fit in my build?

OK.
I would avoid the Corsair CX/VS/CS/Builder series,they are poor quality.
I would get the Gigabyte GTX 970,it's the best card for the price.
I would also get a new PSU when you save enough money,like the XFX Core 550W/Antec HCG 520M/Rosewill Capstone 550M/Seasonic S12II Bronze 520W.The CX600 will be enough for now,but upgrade ASAP. :)