Kid Info 
http://www.kidinfo.com/american_history/explorers.html
This is the site.  It contains biographical information on explorers plus links to other sites.

   Discoverers Web  
http://www.win.tue.nl/~engels/discovery/
Has detailed information on most of the explorers of the New World.

   European Explorers Resources on the World Wide Web http://www.stemnet.nf.ca/CITE/explorer.htm
This is just one aspect of this far-reaching website created in Canada for educational purposes.  The section on explorers has short biographies of all the major explorers and links to other sites.

The Mariner's Museum
http://www.mariner.org/educationalad/ageofex/index.php
This very inclusive site covers explorers from the ancient Egyptians through the Vikings to Magellan and Columbus.