The web has an unbelievable array of resources relating to conservation.   Rather than attempt to provide yet another huge list of sites, I've focused primarily on high-end sites that provide both good information and lots of useful links. I update the list frequently, so keep checking back! 
 

• Academic Programs in Conservation Biology This is a search engine provided by the Society for Conservation Biology; it allows searches by program, keyword, and more. 
• The Center for Conservation Biology at Stanford University has good information on specific projects as well as links to other resources. Paul Ehrlich is the director of the center, if that helps pique your curiosity! 
• Conservation Ecology is a peer-reviewed electronic journal published by the ESA and the Resilience Alliance. 
• ESA, The Ecological Society of America is a professional scientific society dedicated to all aspects of the study of ecology, including conservation-related issues. Among the offerings from their very rich site is an e-mail "news alert" for important enviromental legislative issues. 
• The ESA and the National Science Foundation support the  National Center for Ecological Analysis and Synthesis in Santa Barbara, CA.  Their web site includes information for researchers and community members on a variety of applied ecological topics.
• The American Association for the Advancement of Science sponsors the Program on Ecology and Human Needs, which "seeks to disseminate            knowledge from the sustainable and environmental sciences to                      audiences around the world".  An on-line library includes valuable publications on population, water resources, and more.
•  The Society for Conservation Biology is the one of the pre-eminent scientific society in this field. Their page includes information about the society, a newletter and discussion forum, and lots of other links. 
• Many professional scientific societies devoted to specific groups of organisms provide information on conservation.  For a list of such societies devoted to various groups of vertebrates, check out the list from my Vertebrate Zoology home page.

• American Forests - People Caring for Trees & Forests since 1875 
• Bat Conservation International
• Cetacean Society International
• The Dian Fossey Gorilla Fund International 
• EDF -- Environmental Defense Fund WorldWide
• Greenpeace International Homepage
• Climate - The Debate with Industry - Countering The Sceptics
• Greenpeace USA
• JGI | Welcome to the official Jane Goodall Institute Website 
• The League of Conservation Voters 
• National Environmental Scorecard 
• The Mammal Society (Britain)
• The Mountain Lion Foundation
• National Audubon Society
• National Wildlife Federation
• Natural Resources Defense Council
• The Nature Conservancy
• NatureServe (an organization that, in conjunction with The Nature Conservancy, provides information on rare and endangered species and ecosystems; their website has tons of cool information)
• Rainforest Action Network
• Sierra Club
• Union of Concerned Scientists
• The Wildlife Society
• World Resources Institute (WRI)
• Worldwatch Institute
• World Wildlife Federation
• World Wildlife Fund - US

• Virginia state agencies
• Virginia Department of Conservation and Recreation provides information on state parks and a variety of conservation issues.
• Virginia Department of Game and Inland Fisheries has information on a variety of game and nongame topics.
• VA Natural Heritage Program Home Page is our local heritage program site; the program itself is a cooperative venture between state government and The Nature Conservancy. In addition to information about protected species and species of concern in VA, you can link to heritage programs in other states. I find this a useful way to begin looking for information on specific regions. 
• Wildlife Watching - Virginia Department of Game & Inland Fisheries Online has some good information on game species and related items.
• The Chesapeake Bay and related topics
• Cheasapeake Bay Consortium
• Chesapeake Bay Activities (USGS)
• The Chesapeake Bay Trust
• The Elizabeth River Project

• The Environmental Protection Agency
• EPA Global Warming Site
• Acid Rain
• The National Oceanic and Atmospheric Administration
• Coral Health and Monitoring Program
• Coral Reef Bleaching maps and related information
• The National Marine Fisheries Service
• The National Marine Sanctuary Program
• The NOAA Central Library
• The NOAA Photo Library (awesome pics!)
• The U.S. Geological Survey
• Breeding Bird Survey Summary and Analysis (fabulous site with tons of data and general information on US bird populations over long periods of time)
• The  National Biological Information Infrastructure is a consortioum of federal, state, and local government agencies and a variety of private groups.  Their home page provides links to a huge array of good resources, including
• the Invasive Species Home Page 
• FrogWeb, devoted to the issues of amphibian decline and malformation
• National Mapping Resources
• U.S. Fish & Wildlife Service
• America's National Wildlife Refuge System
• The Endangered Species Program
• Fisheries and Habitat Conservation
• US Global Change Research Program 
• U.S. National Assessment - The Potential Consequences of Climate Variability and Change.

• The Convention on International Trade in Endangered Species, including all appendices and related information. 
• IUCN, The World Conservation Union A consortioum of state, governmental, and other agencies, the IUCN's mission is "To influence, encourage and assist societies throughout the world to conserve the integrity and diversity of nature and to ensure that any use of natural resources is equitable and ecologically sustainable."  See especially
• IUCN Species Survival Commission
• IUCN Red Book (searchable)
• SSC Specialist Groups (groups dedicated to individual species)
• World Commission on Protected Areas
• People and Plants Initiative.  A collaboration between UNESCO, the World Wildlife Federation, and the Royal Botanical Gardens at Kew, this initiative promotes ethnobotany, community development, and conservation efforts world-wide.
• The United Nations
• Food and Agriculture Organization (good information on forests, fisheries, sustainability, etc.)
• United Nations—Economic and Social Development (huge amounts of excellent information, especially related to population growth, resource use, and development issues important to conservation and biodiversity) 
• United Nations Environment Programme
• UNEP World Conservation Monitoring Centre maintains a huge database on endangered species and other important conservation information.
• Threatened Animals of the World is a searchable database, parts of which are shared with the IUCN Red Book.
• Intergovernmental Panel on Climate Change (IPCC) report

• Ecology and Biodiversity
• Environment
• Biodiversity and Biological Collections WWW Server 

• Monterey Bay Aquarium
• Smithsonian Natural History Web Home Page
• Smithsonian National Zoological Park Conservation and Research Center
• Royal British Columbia Museum: Endangered Species in Endangered Spaces

• Declining Amphibian Populations Task Force (DAPTF) is the best on-line collection of information on the complex causes and consequences of this puzzling phenomenon. 
• ESRI Conservation Program: conservation geography, activism and multicultural social change : important resources from the folks who developed ArcView and ArcInfo GIS software.
•  FIU Everglades Interactive Learning Case Study is a nice tutorial and information site about a wonderful ecosystem.
• Red Wolves / Database is an outstanding site that includes on-line mapping of individuals in one population.  Awesome!
• The Woods Hole Oceanographic Institution presents the  "Red Tides" and Harmful Algal Blooms page, with a wide range of information --from single algal species to patterns of HAB incidence over time--on a problem that is becoming incresingly severe. 
• VEGETATION MAP CHECKLIST 3 is a list of on-line vegetation maps, many of which illustrate changes in vegetation type and cover over time in various kinds of communities throughout the world.