Alexander Keith's India Pale Ale (why is it the beer companies that always have the best commericals?)
Wendy's "Ranch Tooth"
That cat that holds his breath, cheeks puffing out because his litter box is so stinky
An old one - "A day in the life of Ronald McDonald"
The Mazda commercial where there's a bunch of guys dressed in black laying down and the leader says "Everybody up, look alive guys". They all stand up, arms up... turns out they're all arm hairs on a guy driving a Mazda.
The Serta Counting Sheep
And radio commercials:
The Ikea guy, particularly the commercial where he says that at the Ikea sale you can save hundreds, possibly thousands, of dollars. "Then with all that money you save, you could buy hundreds, possibly thousands, of 1-dollar breakfasts at the Ikea restaurant."
myautosales.ca - There's a guy in the shower singing "My auto sales.ca..." - turns out he's happy because he just sold his car and bought a new one on that site. As he's singing you hear a thump/crash, then the announcer says "Two rules in life - check out myautosales.ca for your next car, and don't dance in the shower!" (Guy in the shower says "Owwww")
City Cab - the phone number is 717-7777, a number that's easy to remember *anytime*. There's a guy who sounds drunk talking to his drunk friend, wondering how they can call a cab. He tells him to call City Cab - you just dial 717, then keep pressing 7 until someone answers. He tries it, saying the numbers out loud... "7 1 7, 7 7 7 7 7 7... 7?" A City Cab person answers while he's still dialing. "Dude, we're in!"