Everyone loves dragons. Fictitious ones. As Ben Radford notes here, there are some bits of fact mixed with the fun. One comes from paleontology: bones of dinosaurs and giant prehistoric mammals were naturally ascribed to monsters, especially those already established in such sources as the Bible's Old Testament. Another source is the exaggeration of real creatures, such as crocodiles. Naming the world's largest lizard the Komodo dragon is a demonstration of the fascination we have with such creatures. (Douglas Adams wrote that his mind reeled when seeing one on display- "...ten feet long and a yard high is entirely the wrong size for a lizard to be.") In modern fiction, J.R.R. Tolkien gave us Smaug, plus occasional references to "worms" with names like Scatha and Ancalagon the Black. Anne McCaffery gave us the Dragonflight books, and dragons appear in countless other stories (to cite one of the more obvious examples, see the Dungeons and Dragons games and books). In Chinese folklore, dragons were wise and snakelike: in European tales, they had batlike wings and died out at the hands of Saint George and his kind. (The European dragon, incidentally, is almost always drawn with unrealistically small wings for any living creature, compared to the body size: when Chinese dragons fly, they do it by magic and dispense with the whole business of wings.)
Real modern dragons? Well, without dinosaurs in the world (with apologies to some fellow cryptozoologists, we're not going to find live dinos of any sort in Africa or anywhere else), crocodiles and Komodos are the best we have. And occasional "dragon photographs" circulated on the Net are beyond silly. The sirrush, that odd dragonlike creature on Babylon's Ishtar gate, is interesting, though there's no reason to suppose it real. Maybe it, too, was born of the imaginative interpretation of dinosaur bones. Modern studies of dinosaurs have given us creatures so fantastic that they outshine their make-believe counterparts.
So we had dragons. We just came along too late to see them.
P.S. In addition to a new book Ben mentions, Karl Shuker wrote a splendid dragon book.