I own both the 18-105 and 16-85 and I generally agree with Stan regarding their comparable image quality. I had three specific reasons for getting the 16-85, none of which may be relevant to you: (1) I find that the difference between 16mm and 18mm at the wide end is significant for the kind of photography I like to do; (2) I strongly prefer the metal lens mount of the 16-85 to the plastic mount of the 18-105; and (3) I wanted a main lens with focus distance markings on the lens barrel for setting hyperfocal distance, especially in the dark. Reason #3 is mainly relevant to landscape photography, especially low light/long exposure stuff. If these reasons are not important for you, the 18-105 lens is a good performer and a great bargain.
I carry the 16-85 as part of a multi-lens kit that typically includes an ultra-wide zoom (Tokina 11-16) and a telephoto (currently 70-300VR). However, I still keep the 18-105 and have used it when I want to carry only a single lens to take advantage of its additional telephoto reach.