I have to agree with BirdDog, for nature close-ups you can't beat the 200/f4. The added working distance is great.
As for 60 vs 105, the 105 used to double as a good portrait lens, albeit a bit overly sharp for portraits. This is a non-issue in the digital age of course. I've never quite understood the market niche for the 60. It isn't a flat-field macro lens, hence cannot be used on a copy stand (like the 55). I thought it was too short for a lot of nature close-ups. The only thing it had always going for it was its incredible sharpness in the macro range (I think it's so-so otherwise). I would have gone for the 105 any time.
Nowadays (after the 1.5 inflation) the 60 appears to occupy the short range portrait spot the 85 used to hold, while the 105 gets pushed out rather far. So it becomes a little harder to choose between them.
The coolest macro lens in the Nikon range at the moment is the 85/f2.8 PC IMHO. Its tilt ability gives incredible flexibility for macro product shots. It is also flat-field. Now, *that* would be a ripper lens to fondle at a mini-meet
I agree with Walter, too, good close-up lenses are a very handy way to go macro. The good achromats (like the Canons) don't sacrifice image quality. Plus, you don't lose any light as you do with tubes and macro lenses (which are lenses with built-in tubes). No need to buy big sizes, either. Just buy the 52mm and use a step-down ring on larger lenses.
Cheers
Steffen.