The most academic of the general encyclopedias, Britannica Online contains biographical information on individuals from all time periods and nationalities.
Wikipedia can be a great place to get started--just remember that the information can be questionable. Be sure to consult the bibliography at the bottom.
American National Biography contains over 17,000 biographies of deceased Americans whose lives have shaped the nation. (Restricted to 5 simultaneous users.)
A multicultural biographical source that covers notable individuals from every part of the world and from all time periods who have made significant contributions to human culture.
The Oxford Dictionary of National Biography contains a collection of 55,000 specially written and illustrated biographies of people who shaped the history of the British Isles and beyond, from the earliest times to the year 2003. (Restricted to 3 simultaneous users.)
