it all really comes down to your budget and expectations.
at 1080p, if you really wanna max out EVERYTHING then a 280X or 770 is the minimum requirement, save for your resource heavy games like Crysis 3 or Watch Dogs every now and then.
if you feel like you can compromise a tad bit every now and then going for high over ultra, then mid-end to lower high-end cards like the GTX760, 280, 270X, 270, 265, etc. are worth their price. the following cards are also great for 1600x900 res if that's what you have.