I know everyone's familiar with this site, but I still love it. It tells you the #1 song on any day of the past--so people like to do it for their birthday, wedding day, child's birthday, etc.
My birthday: "Daydream Believer," the Monkees
Senior prom: "Don't You (Forget About Me)," Simple Minds
High-school graduation: "Everybody Wants to Rule the World," Tears for Fears
Our wedding day: "Dreamlover," Mariah Carey
Kelly's birthday: "Crank That (Soulja Boy)," Soulja Boy
Day Kelly was actually due: "Kiss Kiss," Chris Brown
Day we moved to Seattle: "Fallin'," Alicia Keys