Of the marketing tools Wizards of the Coast used early in the 4e advertising process, my favorites were their short and humorous cartoons. The Tiefling and Gnome cartoon is still on my list of "pick me ups" when I need a good giggle because my day is a bit glum.
"I'm a monster...Rawr!"
On a side note, the Tiefling appears to be from the Bay Area. (Who else says Hella?)
I don't know that the most recent entry, Red Box Ninjas, is as universally funny -- but it does have a certain resonance with me as a Dungeon Master. We've all had groups like the one depicted in this cartoon.
I couldn't resist putting in this old TV commercial advertising the boxed set that got me hooked.
Or the always hilarious 8-bit Theater bit.