Ancient Footprints: Cultural Diffusion in Pre-Columbian America

When we think of the "First Americans" we generally tend to think of the American Indian. After all, there is no doubt that the Indian has lived in North America for thousands of years, descended from those original explorers who trekked across the Bering land bridge. At least this is what we are taught in school. But is this entirely correct? Were there others that came perhaps before and during the original population of North and South America by those that would later be called "Native Americans"? Were there others that embarked on expeditions to the mysterious lands to the west (or east) that brought not only trade goods but knowledge and ideas of other religions, cultures and oral traditions?