Goodbye Jay Leno and hello Jimmy Fallon. The new host of the Tonight Show opened his first monologue with just one promise: "I'm Jimmy Fallon and I'll be your host… for now."  He then thanked all the hosts who have come before him before deciding to celebrate by getting his groove on with Will Smith:



And if we know our Jimmy Fallon, you can expect more musical numbers coming your way. Here's a look back  at some of the best musical performances from his previous Late Night gig: