I know the answer to this is generally aftermarket, since it's usually only $30-50 more, but...
At the moment I can get a reference GTX 980Ti for £500, an Inno3D Herculez (not the iChill X3 one) for £525, or an MSI Gaming 6G for £600. I'd like to moderately OC (to 1300-1400mhz core if possible)...