I've got a full size graphics card in now in the one below
Gigabyte Radeon R9 280X Rev2.0 WindForce 3X OC 3072MB GDDR5 PCI-Express Graphics Card with Battlefield 4 PC Game
Full size could mean anything from 15cm long right up to 35cm. Still recommend the tape measure, then you can pick and chose best card that will fit

I also did some very quick power calculations and given that the Maxwell gpu (GTX970 and GTX 980's) is so power efficient, you could probably slap a GTX980 in your box without even having to upgrade your power supply.... So pretty much the fastest single GPU graphics card that's currently available..... In theory your PC with a GTX980 fitted would only be pulling about 400 watts so you even have a bit of leeway!
Price wise, the best bang for your buck is the GTX970, but best card for performance is the GTX980... Personally I'd keep to the Nvidia's for now until the next gen AMD cards appear. Performance aside, they really seem to be winning on the lower power consumption and therefore lower heat output which is a big factor in an ITX build.
E-I