A 2007 Caldecott Honor Book, Gone Wild: An Endangered Animal Alphabet is both innovative -- with its black and white cut-out-like illustrations -- and informative. Many children in the 2-4 range already know what an alligator, a boa, a duck, or a flamingo look like, but do they know what a Chinese Alligator looks like? Or a Tree Boa? or a Blue Duck? Or an Andean Flamingo? If you've never heard of these (and especially if your children haven't) then you've discovered the right intro book.
My only reservation is that while the letters are nice and big and captivate the eye, the small endangered animals in red are small---and because they are in red the child doesn't get the full sense of what these animals actually look like. Apart from that, I think it's a great introductory book to endangered animals, and also shows an alternate side to multi-colored illustrations.