I found the genealogical database on Obama compiled by William Addams Reitwiesner at WARGS. It is exhaustively complete, tracking known information as far back as his great-great-great-great-great-great-great-great-great-great-grandparents in the 17th century.
If your family name (or that of a friend) is Dunham, Armour, Payne, McCurry, Clark, Wright, Childress, Black, Abbott, Clemmons, Donovan, Poland, Davis, Taylor, Wilson, Jones, Thomas, Godfrey, Williams, Smith, Walker, Martin... etc etc you may want to check out the list for possible connections.
I didn't find any obvious links to my ancestors, but of course, once you go back that many generations, we're all related.
WARGS also has geneaologies for European Royalty, European Nobility, and other US political figures (Biden, Bush, Cheney, Clinton, Gore, Reagan, Bush, Quayle, Agnew, Mondale and cabinet officers and governors (Sarah Palin, Jesse Ventura) and senators and representatives and many others.