Australia: Department of Sustainability, Environment, Water, Population and Communities: Environment Protection and Biodiversity Conservation Act Lists
United States: U.S. Fish and Wildlife Service : Endangered Species Program
European Commission: European Red List
NatureServe (United States and Canada): NatureServe Explorer
While many countries and regions moniter the populations of the animals around them, not all of them make the results easily accessible online and/or in English.
The IUCN Red List, the main resource for global information conservation status, has nine conservation categories.
Two categories do not indicate the species' conservation status:
Not Evaluated is the status for species for which no threat assessment has been done yet
Data Deficient is for species for which a threat assessment has been done, but has been judged to be not usable to establish the conservation status.
There are two pre-threatened categories:
Least Concern species are not threatened and unlikely to be.
Near Threatened species could become threatened species if their situations continue.
There are three threatened categories:
There are also two categories for extinction.
Extinct in the Wild species can only be found outside of their natural habitat, such as animals in zoos.
Extinct species are no longer.
From the IUCN Red List. More information about the categories is available here. IUCN has updated their conservation categories and corresponding criteria twice since they began, most recently in 2001. They also reevaluate animals on a regular basis.