I recently discovered the University of Connecticut's web site on plants at

http://www.hort.uconn.edu/plants/

There is a wonderful "Plant Selection" section that allows you to put in the information you need to select a plant. For example someone was looking for a vine that was native and would grow in zone 5 in a partially sunny spot. I put in this info and came up with 6 possible choices.

It also identifies potential invasive plants in the plant descriptions. Very useful site.