Dodo stamps.

Pib Burns' fascinating homepage covers topics like cryptozoology and astronomical catastrophism, but I especially like his collection of dodo-themed postage stamps. While the birds have been extinct since 1681, they're the continuing source of fascination by stamp collectors and explorers alike (William Gibbons, upon hearing rumors that dodos were spotted in the island of Maritius in the Indian Ocean, mounted an unsuccessful expedition there in the 1990s). Marituius, Laos, Cuba, and Micronesia have all produced commemorative stamps.