10. Will It Float? (Late Show with David Letterman)
When it debuted: 2002
Segment lowlight: The third installment, when Dave said, "We've only done this three times. Nobody on the show really likes it. From your cards and letters and phone calls, we know that you folks at home don't care for it, either. We're gonna try it one more time, and if it's not anything tonight, that's it." And then he proceeded to do it 200 more times.
We bet you can guess the premise of this one. Throw something in water and see if said thing floats. Somehow this bit lasted more than five years, during which time the show produced over 200 installments. For reasons surpassing understanding, someone has made a "Will It Float? Fan Page" cataloging the over 200 times the game has been played. For those hoping for a deeper study, the creator of the site also includes links to "Achimedes" and "bouyancy" on Wikipedia. Thanks, dude.