Well since we're not counting the Japanese commercials, I'd have to say that one of my favorites was for Outpost.com They had a great, twisted advertising campaign going. Their first one was where they fired a gerbil from a cannon through the "O" in their company name. The second one, they released a pack of ravenous wolves on a high school marching band.
I really loved these commercials, and the old announcer guy in them ruled. I couldn't find the wolves one, but
here's the Gerbil Cannon one. You're better off right-clicking to save it to your computer, cuz it's about 10 megs in size and doesn't stream very well.