Nikon AF-D 2.8 18mm
I have always used this lens on a full frame camera, D700 and D3x. On a D800 the lens needs some stopping down for best edge sharpness, but at any aperture it performs much better than a 20mm. So if you need a compact wide, it's a fine lens.
As I have a 14-24 it will not be used very much, when I want to go light I take my GX1 and 9-18mm.