1421: the Year China Discovered America by Gavin Menzies covers the exploration of the world by the Chinese treasure fleets between 1421-3. The Chinese mapped (parts of) the coasts of South America, Antarctica, Australia, North America, some islands in the Caribbean, and, surprisingly, Greenland. That wasn't really new information, since the European explorers who came later used maps that contained areas they had never seen. Why don't we learn this in school? Not only did Columbus not discover America, and Magellan not "discover" the Straits of Magellan, but we never even knew about it. The Chinese dynasty that sent out the treasure fleets came to an end soon after the fleets returned from their explorations, and the new dynasty destroyed almost all information from these voyages and began a period of isolation from other parts of the world. This book is really eye-opening. Some parts of it certainly drag a bit, and there isn't necessarily enough evidence to support some claims made in the book, but overall it is an intriguing look at history.
If you're interested in the book, check out the corresponding website, http://www.1421.tv/, which has the latest info on the ongoing research and discoveries of evidence of the Chinese around the world.