What's your favorite commercial featuring an actor from Seinfeld (either a regular or supporting player)? There are so many to choose from: Jason Alexander's "Pretzel Boy," Michael Richards for Pepsi, Julia Louis-Dreyfus for hair care, Jerry himself for American Express--even Patrick Warburton (Puddy) in a Cadillac spot.
Personally, my favorite is Wayne Knight's Frosted Cheerios spot, part of "this box never closes" series. He is positively Newmanesque at the end, when he yells "Jackpot!"
A close second is a brief (10-second) regional spot for the Marriott Marquis Hotel in New York; Jerry Stiller and Estelle Harris (you know them as the Costanzas) argue off-camera whether they are to go see "Les Miserables" or "Phantom Of The Opera," while a small pug dog resignedly lies on a chair. He's apparently heard it all before.
Let's hear your favorite--or least favorite.