Best Nikkor lens for my Nikon D90?

Happy with my D90 camera with 18-105mm lens.
I consider a good start in macro photography, with Original Nikon lens, best suited for my D90.
Activity will be like flower close ups, and occasionally insects.
Appreciate guidance; thank you.
Alternative might be a compact system camera with a dedicated macro lens?
Rgds
Guido

I suggest looking at the Tamron SP 90mm f/2.8 Di VC USD 1:1 Macro lens. Here is a review:
http://www.dpreview.com/..._90_2p8_vc

There's also an excellent hands-on review in the Feb. 2014 issue of Shutterbug Magazine.

I'd recommend the Sigma 50mm f2.8 macro, or if you need a little more distance between you & your subject, the Sigma 105mm f2.8 macro.

Both are excellent, tack sharp lenses.

Here's a shot of dragonfly eyes I took with the 50mm f2.8 on my Nikon D300;

I used to own a D90 (it was gifted to my eldest son when I bought a D7100). I have had great luck with the Tokina 100mm f/2.8 macro on the D90. It is one of the least expensive - but high quality macro lenses you can buy.

One thing about the 100mm range. The DoF at macro distances is wafer-thin, and you may find that you need to stop the aperture down to get any kind of depth (the Tokina will go to f/64). For this reason, you will at minimum need to use a tripod, and ideally a macro flash.

A less demanding lens is the Nikon AF-S 40mm f/2.8 micro. While it is too close for bugs, it works well for macro in other instances, and you can usually hand-hold the camera with this lens, without the need for a tripod or macro flash. The DoF is not as demanding either, and it's a lot less expensive for getting into macro with this lens.

My wife is very happy with her 85mm Nikkor Micro lens (micro is Nikon's name for macro). It is lightweight, reasonably priced and high quality. It also doubles as a very good portrait lens.

Don't go for a 40mm or 50mm lens for photographing insects. You will need to get too close to our subject and end up blocking your light with your own body as well as having more chance of spooking the insect. In general the best advice is to buy the longest micro/macro lens that you can afford, but once you go much over 100mm the prices do seem to rocket.