The Neotropical Team at Kew have developed this interactive key to plant families of the Neotropics (you will need Java to run this key):
http://www.kew.org/science/tropamerica/neotropikey.htm
This key was built using Lucid software. A free version is currently available:
http://www.lucidcentral.org/Software/Lucid3/Lucidv33FreeOffer.aspx
Institut de recherche pour le développement