My current favorite is definitely "The Pepto Bismol Macarena".
I also love Venus's recent one at the arcade for American Express.
Sorry, smurfie, I'm not a fan at all of Geico's or Six Flags's. But I do love Oscar Meyers: "My bologna has a first name: O-S-C-A-R. My bologna has a last name: M-E-Y-E-R-S. Cause Oscar Meyers has a way with B-O-L-O-G-N-A."
I'll think of more later...