One of the ways we made our wedding reception unique was by having controlled karaoke. I organized a flash mob of "Seasons of Love" from Rent, which set things on a great trajectory. We asked several friends to sing, and we had YouTube and a video monitor available for them so we didn't have to pay for "real" karaoke. We just asked them to run the song by us first.
One of the best moments was our flower girls singing (and dancing to) "What Makes You Beautiful."
Here's a link - it's hysterical! And the dancing wasn't planned, lol.