Dave Czaplak of Maryland, USA, has some very good pages on Moths and Butterflies, (http://odolep.com/
) but the most impressive parts of his site are on odonata--so I wanted to be sure to put a link in that category. (I've put as the main link above his page on damselflies.) He has done some beautiful drawings of damselfly abdomens--very useful in identification.
The pages on odonates are:
ID Page for Mosaic Darners in MD
ID Page for River Cruisers in MD