"Plant taxonomic keys repository" by S Nordin, MS Baba, and K Itam. Paper from 2011 International Conference on Research and Innovation in Information Systems (ICRIIS), November 23-24, 2011

The Royal BC Taxonomic Collection (online) - from Fisheries and Oceans Canada and The Royal BC Museum.  At this point all entries are for animals.

ITIS Integrated Taxonomic Information System- Taxonomic information on fungi, plants, animals, and microbes of North America and the world.

Taxonomy database and resources from NCBI