|Social Security Application Form|
The collection has data from over 49 million people and often lists the applicant's father's name and the mother's maiden name! If you haven't had much luck finding or confirming a relative's parents, now is your chance.
It is also a good quality source for date and place of birth as most people are less likely to lie about their age on an official government form. They still might fudge, but it's a good solid clue -- and that's what being a cousin detective is all about: clues.
Now that you know about this great new source, try not to be too offhand and smug when you casually drop the inevitable, "have your tried searching Ancestry's Social Security Applications and Claims index?" Just smile graciously when their second great grandparent's names appear on the screen as if they were common knowledge.