FamilySearch, the online arm of the Family History Library, has a new beta search service that lets the public dig around to find documents and facts on their relatives and ancestors. It's a pretty huge index of data, and it's free.
The library contains a vast amount of historical records and tallies from all over the country and world. Census data, birth and death certificates, church parish tallies, military enrolments and many, many more data sources. If you've ever been intrigued about those who came before, but don't want to invest your time quite yet in a family tree app, taking a peek around FamilySearch might pay off
It's a service run by the Church of Jesus Christ of Latter-Day Saints, and it's free to browse and use.