Jimmy Fallon headed corss town to the Ed Sullivan Theater to be on the "Late Show with David Letterman." The conversation was one of those curiously-awesome moments of late night television, with the always-charismatic Fallon paying his respects to Letterman in the same way a mob underling kisses Don Corleone's ring. There's some good banter about Letterman's old studio at 30 Rock, 6A, and a great story about Jimmy Fallon's run in with Bruce Jenner at the London Olympics. But the highlight of the night was Fallon picking up his guitar and harmonica to sing the "Fresh Prince of Bel Air" theme song in Neil Young's voice.