The Meaning of America: Discovery, Encounter, Invention
 
Columbus and the Age of Discovery
http://www.millersv.edu/~columbus/
This comprehensive site, hosted by Millersville University, offers a wealth of information on explorers, first contact, and the age of discovery.  It includes the full text of a wealth of articles, chronologies, students papers, links, and more.

The Columbus Navigation Homepage
http://www1.minn.net/~keithp/index.htm
This site, from Keith A. Pickering (a computer systems consultant and historian), provides information about various kinds of navigation, plus a number of maps, detailed information about the voyages of Columbus, and a section on the problem of determining where Columbus made landfall in his journey.  There are links to lesson plans that use this site.

Aztec Account of the Conquest of Mexico
http://www.fordham.edu/halsall/mod/aztecs1.html
From the Internet Modern History Sourcebook (http://www.fordham.edu/halsall/mod/modsbook.html), this site provides the text of the speeches of Motecuhzoma and Cortés.

Discoverers Web
http://www.win.tue.nl/cs/fm/engels/discovery/
This page by Andre Engels, a Ph.D. student in mathematics and computer science in the Netherlands, includes links to many pages on explorers, from prehistory through nineteenth century explorations.  There are links to maps, timelines, and historical pages covering ancient Rome, the Americas, Asia, Africa, the Pacific, the Islamic world, and more.  A truly impressive collection of resources.