I think the Nikon 200-500 should be on anyone's short list. I have heard great things about it. Take a look at the Sigma and Tamron 100-400 lenses. Both are new, and both are light and reasonably priced. I just got the Tamron, and so far I am impressed. The Tamron and Sigma 150-600 offerings are very good lenses for the money, as well. Several people on Nikonites own one or the other, and we all seem reasonably happy with them.
I would avoid the older, used mega-zooms. It's not that they are all bad lenses, but the technology has advanced to the point that you can get a new and better lens for not that much more money. Just my perspective, of course.
I would avoid the older, used mega-zooms. It's not that they are all bad lenses, but the technology has advanced to the point that you can get a new and better lens for not that much more money. Just my perspective, of course.