If you have ancestor data in familysearch.org then you should try out relativefinder.org.
Relative Finder looks through your family history and the family history of famous people, looking for common ancestors. Some of the selectable categories for famous people include:
- Catholic – Saints and Popes
- ( U.S. ) Constitution Signers
- European Royalty
- LDS – Prophets
- Mayflower
- U.S. Presidents
When you go back far enough your shared ancestors can make some really interesting connections.