Land Protection
Many governments have been quite active in preserving natural areas. If effort is measured by the percentage of the natural landscape protected, the little country of Costa Rica in Central America would be a winner. NGOs generally preserve land by using privately donated funds. The Nature Conservancy is the non-governmental organization that has probably preserved the most land worldwide. The Trust for Public Land (TPL) focuses on preserving natural areas in America. The Peninsula Open Space Trust has been active in the San Francisco Bay Area.
International Advocates
The World Wildlife Fund aims toward saving endangered species, protecting endangered habitats and addressing global threats such as toxic pollution, over-fishing and climate change. Conservation International works to conserve the Earth's living heritage, our global biodiversity, and to demonstrate that human societies are able to live harmoniously with nature. The Global Forest Watch purpose is preserving the remaining natural forests worldwide.
North American Advocates
The Wilderness Society advocates wilderness preservation in the United States. The Wildlands Network works to reconnect the continent with vast pathways that tie natural places together. Within each 'MegaLinkage' it proposes regional systems of connected protected areas - mosaics of public and private lands that provide safe passageways for wildlife to travel freely from place to place. The Rewilding Institute advances continental-scale conservation through four megalinkages in North America, particularly the need for large carnivores and a permeable landscape for their movement.
Information
The IUCN Partnership maintains a Redlist - a database of endangered species throughout the world. The World Wildlife Fund has a map-driven, searchable database of more than 26,000 species worldwide, with a powerful search tool to find (1) where specific species live or (2) what species live in specific places. Conservation International maintains information on biodiversity hotspots around the world. World deer provides information on deer species throughout the world. Wilderness.net provides a database regarding wilderness in the USA.