For some reason, I enjoy the ones for Dos Equis beer with the most interesting man in the world. “I don’t always drink beer, but when I do, I prefer Dos Equis.”
Two of my favorites have already been listed: the Snickers great googly moogly ad (I used to have that phrase as the shutdown sound on my computer) and the Bacardi Fly. Two more I love are the Snickers Batman ad and the Gamestop Bunny. Man, I could watch these commercials all day.
You got a problem with him stretching the Golden Pipes? 
My faovrite is the one where he rents a clown.
“I seriously underestimated the creepy factor.”
Harr! I get to post a link to our beloved romance hero, Sebastian!
The one where the hick guy in high class company says “wouldja please pass the jellly” and people start fainting over his faux pas, for Pollaner All Fruit, is an oldy but goody. Still can give me a chuckle.
I, too, LOOOOVE the e-trade baby and the small girl that makes the slideshows about windows 7 (I lose it every time the kitten in the field of marshmallows comes up).
I’d also like to add:
Head and Shoulders with Troy Polamalu
Guinness St. Patrick’s Day spot
Mike’s Hard Lemonade “It’s cold” spot