FamilySearch.org lets you tap into the world’s largest family history database, maintained by the Church of Jesus Christ of Latter-Day Saints. The library contains millions, if not billions, of records from the United States, Canada, the British Isles, Europe, Latin America, Asia, and Africa. Users can search by geographic location, surname, or specific ancestors, then post discoveries to the Share My Genealogy boards.
In addition to a vast reservoir of family history information, http://www.genealogy.com also offers free software that lets you create a personalized family tree. The information you compile is formatted into a hyperlinked index that you can download to your computer, save at the site, or post to the World Family Tree. You can also search through the family trees of such famous figures as Daniel Boone and George W. Bush to see if you share common ancestors.