The following are powerful tools and information resources for tracing family roots and doing genealogical research on people in history:

Ancestry.com Free and fee-based access to 600 million records from 2,500 databases.
Cyndi's List More than 66,000 links in 120 categories including African-American, Native American and Jewish records.
FamilyHistory.com An online genealogical community featuring more than 130,000 message boards.
Family Search The extensive world wide database sponsored by the Church of Latter Day Saints.
Genealogy.com A variety of genealogy services including resources for teachers and students.
Gengateway.com Guides, gateways and software for constructing family trees.
National Genealogical Society Resources and services from this society.
RootsWeb Resources from the "oldest and largest free genealogy site."
USGenWeb Project Genealogy records organized by counties and states.
WorldGenWeb Genealogical records compiled for regions throughout the world, including the British Isles and the Caribbean.