I would like to get some advise on what lens to get.
I have a Nikon D300 with lenses, 70-300mm AF VR , 50mm F1.4AF and 35-80mm AF.
I would like to shoot close-ups of insects and flowers. The lenses I have now don't do that.
For insects, you'd probably want a macro lens in the 90 or 100mm range. No zooms. Look into the Nikon for price, and then the Tamron 90mm f2.5, a very highly regarded lens, and built to last. Either one will double nicely as a portrait lens.