What type of macro lens do I need for my Nikon D80 (digital)?

1. I want close range nature photography.
2. I want a good lens for portrait photography.
I would like a lens (or lenses) that could be used on more than one camera (eg Canon and Nikon), but there is little chance I will ever switch to a film camera.

Good advice on the macro and portrait lens selection the only thing I will add is that there IS an adapter to use Nikon lenses on a canon body there is not one i know of to go the other way due to the flange distance

http://www.adorama.com/NVEOSNK.html

http://www.bhphotovideo.com/c/product/197094-REG/Novoflex_EOS_NIK_Lens_Adapter_Nikon_to.html

http://www.kenrockwell.com/tech/roxsen-converter.htm