1. Bruce Willis
Lots of guys have featured comedic bits when they've come on Dave's show — Steve Martin, Will Ferrell, Bill Murray — but nobody so relentlessly brought his A-game as Bruce Willis. Dressing in a Snuggie; trying to do some David Blaine-esque live magic; hawking his new coffee brand, StarBruce; doing an interview while wearing a Sarah Palin wig; participating in a Top 10 list, "Top 10 Ways Bruce Willis Is Spending His Summer"; proving to be the most action-packed Late Show intern ever: No modern star was more willing to make a fool of himself in late night for the sake of a few goofy laughs. In Willis's recent years, his movies have arguably grown progressively lamer. But that didn't matter: We were just happy he kept making them so that he'd have an excuse to go back on Letterman again. When Dave retires, will Bruce, too?