Amphibians on the IUCN Red List (formerly the Global Amphibian Assessment): http://www.iucnredlist.org/amphibians. A valuable website that provides maps drawn by regional experts for all species of amphibians as well as comprehensive information on conservation status. This is a canonical site for conservation information. See Ficetola, Rondinini, Bonardi, Padoa-Schioppa, and Angulo, 2014, J. Biogeograph., 14: 211-221, for discussion of accuracy.
AmphibiaWeb: http://www.amphibiaweb.org/. Largely an aggregator website with information from, e.g., IUCN, iNaturalist, NatureServe, HerpNet, and ASW, although with some original content, which is directed at the informed public and provides information amphibian conservation, population declines, as well as other general information about and images of many amphibian species. The taxonomy employed tends to lag behind the systematics community.
Anfíbios de Colombia: http://www.batrachia.com/. One of the very best websites for one country and because Colombia is a serious hot-spot of amphibian diversity this is a very useful site.
AmphibiaChina: http://www.amphibiachina.org/ (Mandarin); https://translate.google.com/translate?hl=en&sl=zh-CN&u=http://www.amphibiachina.org/&prev=search (English translated page). A website dedicated to providing information on the Chinese amphibian fauna, led by Che Jing of the Kunming Institute of Zoology, China.
Herpetological Taxonomy and Systematics: https://www.facebook.com/pages/Herpetological-taxonomy-and-systematics/751055144919750. A source of recently named species and taxonomic change in herpetology. Seems to do a good job of reporting new taxa.
ARKive. Images of Life on Earth (Amphibia page): http://www.arkive.org/amphibians/. This website is dedicated to informing the public about threated amphibians (and all other threatened species as well) via multimedia. Explore and search for videos, photos, and facts about endangered species. Arkive is an IUCN partner.
Biodiversity Heritage Library: http://www.biodiversitylibrary.org/. A remarkable free online source of biodiversity publications that are out of copyright and many (e.g., KU series) that are still in copyright.
CalPhoto Images: http://calphotos.berkeley.edu. A great resource for images, maintained by Biodiversity Sciences Technology (BSCIT), part of the Berkeley Natural History Museums at the University of California, Berkeley.
The Center for North American Herpetology: http://www.cnah.org/. A site dedicated to providing information on the amphibians and reptiles of the United States.
Encyclopedia of Life (Amphibia page): http://www.eol.org/pages/1552. Potentially an amazing resource, but currently lags behind other websites. The tie-in to the Biodiversity Heritage Library will make this site very useful for professionals.
Google: http://www.google.com/. The fastest way to locate information, albeit disorganized, on any taxon is to search for it on Google. But, like any unvetted information source errors abound.
ITIS (Integrated Taxonomic Information System: ITIS Amphibia record) and the Catalogue of Life: http://www.catalogueoflife.org/). ITIS is a United States Department of Agriculture system for storing information on all organismal names. The Catalogue of Life is a taxonomic summary of ITIS information available through a relatively user-friendly interface. LSIDs of all of the taxon names are available through the Catalogue. This is also the source of the taxonomy employed in the Encyclopedia of Life.
Mikko's Phylogeny Archive: http://www.helsinki.fi/~mhaaramo/metazoa/deuterostoma/chordata/amphibia/lissamphibia/lissamphibia.html . A useful site for access to phylogenetic information and comparisons of different taxonomic arrangements.
National Amphibian Atlas: http://igsaceeswb00.er.usgs.gov:8080/mapserver/naa/. This site contains reasonably good maps of the distributions of amphibians in the United States, although in some cases counties seem to be the unit of occurrence, and without accompanying text it is difficult to evaluate the sometimes significant differences between these maps and those in the more traditional field guides.
Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico: http://www.ssarherps.org/pages/comm_names/Index.php. The recommended English names of the three major herpetological societies in North America (Society for the Study of Amphibians and Reptile, Herpetologists' League, and American Society of Ichthyologists and Herpetologists), with comments on taxonomy.
Translations of the Scientific Names of the Reptiles and Amphibians and Amphibians of North America: http://ebeltz.net/herps/etymain.html. Lots of interesting and helpful biographical and etymological information on USA and Canadian amphibian and reptile names from the indefatigable Ellin Beltz.
Tree of Life: http://tolweb.org/tree?group=Living_Amphibians&contgroup=Terrestrial_vertebrates. This site (not associated with the NSF Assembling-the-Tree-of-Life Program, which marked the rather corrupt end to substantial support of systematics efforts by the U.S. National Science Foundation, which is now funding at something like 4% of received proposals) provides a basic source of information regarding the evolutionary history for all major taxa of amphibians optimized on educational outreach. The contents and badly "under construction" and substantially out of date in most amphibian groups. A great concept, however.
VertNet: http://portal.vertnet.org/. This site ties together collection data for most of the important online herpetology collections. Results, especially the maps, should be carefully interpreted by an expert systematist prior to use for scientific purposes, as collections vary in the nomenclature adopted (or the rate of updating) for purposes of warehouse management.
Wikipedia: http://www.wikipedia.org. The English version is largely a source of taxonomic misinformation and/or dysinformation. (I have tried to fix some of the egregious propaganda, only to find the dysinformation back again the next day, suggesting the anonymous involvement of deeply unethical people.) Caveat emptor! Having written that I must comment on the fact that the French and Spanish versions of Wikipedia (http://fr.wikipedia.org/ and http://es.wikipedia.org/, respectively) seem to be doing a much more responsible job towards taxonomy generally and amphibians specifically than does the English language version.
Wikispecies: http://species.wikimedia.org/wiki/Main_Page. A website that intends to have a page for every taxon. Unfortunately, like Wikipedia, although it is improving, a significant amount of the content related to amphibian systematics is either poorly researched or is simply misinformation by people with big political agendas. Caveat emptor!