The Department of Biology of the University of Trieste is creating a series of interactive keys for the identification of vascular plants from different areas of Northern Italy. The keys, produced by program FRIDA, patented by the University of Trieste, are illustrated with thousands of original pictures. Although they written in Italian, they may be of interest also outside the country, since most characters are illustrated by drawings and pictures. The hitherto available keys are accessible from: http://dbiodbs.univ.trieste.it/dryades/tools/tools.html
I looked around there a bit. The Italian is a bit confusing to me, of course (although I can figure out "foglie" are leaves & so forth), but otherwise it looks like an excellent resource! I haven't seen any web resources this comprehensive and well-constructed for plant ID before! Just too bad I'm not in Italy to be able to really take advantage of it.