Taxonomic Outlines

Systema Naturae 2000 (Domain, 6 Nov 2017)

Websites

Catalogue of Life
The Tree of Life Web Project
Zipcode Zoo
Try Wikipedia

General Search Engines

Bing (Images)
Google (Images, Books, Scholar)
Yahoo! (Images)

Scientific Search Engines & Libraries

Biodiversity Heritage Library (BHL)
Canada Institute for Scientific and Technical Information (CISTI)
Entrez, The Life Sciences Search Engine (NCBI)
Index to Organism Names (ION)
PubMed (NCBI)
ZooBank