The original post ask what lens you use the most and I answered that question for the lenses I have in an earlier reply. This seems to have turned into a "I would recommend this lens thread". There is two very important pieces of information that have not even been mentioned and before I would recommend a additional lens I would want to know two things. First, what is your budget and second, what kind of subjects do you plan to shoot? Knowing what others find as useful lenses is an interesting question but I don't see how it helps you out that much. If you tell us what you would like to be able to take pictures of in the future and what your budget is we might be able to give you some helpful information that YOU might benefit from. Not knowing these answers yet if I were to have to make a suggestion I would go with the Nikon 70-300VR lens. I also own one of these and think that it would compliment the 18-105 pretty well. As I have said I do own this lens and it works very well and is fairly sharp. I also have the Nikon 18-200VR and like it a lot but don't think it would add much to what you already have.
I just want to add that the Nikon 70-300VR will also work on FX cameras as well just in case you move up to one somewhere down the road it will still be able to be used without having to be replaced.
Next up is a 35 or 50 1.8