The Sigma 24-105mm F4 DG OS HSM is a great value for full-frame shooters. It's quite sharp, and although it's on the heavy side, its size makes it a good match for most full-frame D-SLRs, even the relatively compact Canon 6D.
4.4x zoom range; Constant f/4 aperture; Quite sharp; Optically stabilized; Full-frame coverage; USB dock compatibility
Some distortion throughout zoom range