Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
An invaluable site for synonyms, links to original descriptions, literature, and other information. Covers the entire world, but tends to have more complete information for European and North American species. A great place to begin literature searches.

cite:1329955
http://ftp.funet.fi/index/Science/bio/life/insecta/lepidoptera/