A set of full resolution images comparing the sharpness of 12 lenses at the largest possible aperture and at f/8, on a Nikon D200:

Nikon 18-35mm (@30mm) - best corner detail of the zooms, just slightly soft wide open with very good center, f/8 excellent center and very good corners, visible barrel distortion
Nikon 28-105mm (@50mm) - reasonably sharp at both apertures for a zoom, corners good (FX lens on DX camera), very good at f/8
Nikon 24-120mm (@48mm_ - corners slightly softer than 28-105, contrast not ideal, surprisingly good at f/8, just beats the 28-105 in the center
Nikon 18-70mm (@50mm) - contrast well controlled throughout, decent sharpness wide open except corners, very good at f/8
Nikon 18-200mm VR (@55mm) - quite sharp in the center but very soft in the corners, especially wide open, good overall at f/8
Nikon 70-200 f/2.8 VR (@100mm) - dissappointing wide open in the corners (field curvature?), extremely good at f/8 (better than the 50mm & 85mm primes)
Nikon 24mm f/2.8 - decent contrast wide open, consistent from corner to corner, very good at f/8, some barrel distortion
Nikon 50mm f/1.8 - low contrast wide open, excellent at f/8
Nikon 85mm f/1.8 - contrast suffers wide open but still sharp, excellent at f/8
Nikon 105mm f/2.8 micro - extremely good, better wide open than the 50 and 85 primes but not quite up to the Sigma 150 overall
Sigma 150mm f/2.8 macro - extremely good wide open, outstanding at f/8, definitely the sharpest of the lot along with the 300mm (and not a Nikkor, hmmm...)
Nikon 300mm f/4 - extremely good wide open, outstanding at f/8, virtually a tie with the Sigma 150