For further information about recently extinct species you may wish to consult the following internet resources:
IUCN Red List The IUCN's Red List of threatened taxa is widely considered the world's most authoritative. Although predominantly concerned with species which still survive, it nonetheless has a strong representation of species which have become extinct since 1500 AD.
The Sixth Extinction Website (TSEW) The original website about recently extinct species, run by Peter Maas. It contains a wealth of information, including lists of recently extinct species grouped taxonomically.
The Sixth Extinction Forum The biggest and best forum on recently extinct animals, run by Peter Maas. The companion forum to the Vanishing Plants forum, run by Melanie Nayyal. You will need to register an account to view all the threads, but it is well worth the effort.
The Vanishing Plants Forum A forum on recently extinct plants, which are often left out of the discussion on the "sixth mass extinction". You will need to register an account to view all the threads, but it is well worth the effort.
Ausgerrottete Arten-Extinct Species A website listing all of the species which have become extinct within the last c.10,000 years. It is run by Alexander ("Alex") Lang.
The Extinction Website A website run by Francisco ("Frank") Godino. It has a strong representation of recently extinct birds, and includes a special pdf viewer as well as numerous photographs of preserved museum specimens taken by Frank himself at the British Museum.
Lost Amphibians of India The list of amphibian species endemic to the Indian sub-continent which are currently "missing".
Amphibian Rescue A list of all currently missing amphibians around the world, created by the Panama Amphibian Rescue and Conservation Project. The rest of their site is excellent too!
Endangered Species International A spreadsheet type webpage with the names and other important information, including references, of recently extinct species. A tab allows you to switch between animals and plants.
IUCN Species Action Plans A list of all of the IUCN's species action plans. Most are downloadable as .pdf files for free. There is tonnes of excellent information for the conservation-minded reader.
The Bulletin of the British Ornithologists' Club Volumes 1 to 127 are available for free from the Biodiversity Heritage Library (BHL).
Julian Pender Hume's website Many of his publications are available on his website, most of which pertain to recently extinct species.
FishBase A database of most species of both freshwater and saltwater fish. It is regularly cited by both popular and scientific authors.
Zoonomen An online resource for current ornithological taxonomy. Includes many side notes and clarifications of the correct year of publication etc.
The Quest for Thylacoleo forum An excellent forum which has a board specifically dedicated to the discussion of the persistence of the thylacine and Thylacoleo, as well as other Australian and worldwide cryptids.
Save the Bilby Fund Australia's remaining Bilby species (Macrotis lagotis) is highly endangered and threatened with extinction. The Fund aims to raise awareness of the Bilby's plight, and to proactively preserve it through such means as the construction of predator free enclosures, school visits, and the famous (and very yummy!) chocolate Easter Bilby's.