A good starting point might be to review Why Study History? and what you are already expected to know as a high school graduate in terms of National Center for History in Schools, which includes the National Standards in World History and, particularly those for Grades 5-12. There is also an attached webpage on this site giving the homepages for the roughly one thousand history departments which you may wish to contact.  
 

There are usful beginner's guides in the Historians and the Web and the Librarian's Guide to History Resources on the Internet. There are very useful links and subject categories in the the Gateway to World History, as well as the sites posted by the University of Kansas and Tennessee Tech. See too Horus History Links and the webpage on Intellectual History. 

There are also and a listing of History Sites by Time Period. For some specific themes, see the Distinguished Women of Past & Present, a course site for Urban History and the History of Social Invention. 

Considerable documentation is also available through the Center for History & New Media. UC-Santa Barbara maintains large sets of links as "Voice of the Shuttle" for Humanities in general and History in particular. See, too, Rice University Gopher for History Bibliography  

Electronic resources are heavily invested in an important subcategory of history: Genealogy.