My personal favourite:

Double Life - http://www.youtube.com/watch?v=6Bqq38WZctA

Nothing explains better the potential of videogames.

EDIT: I have to add this one: http://www.youtube.com/watch?v=22HXIMASkZo

The idea of mixing a videogame shared universe with Toy Story for games is pure genious.

SONY's marketing department has made some really awesome commercials.

I love this Canon (camera) advert:

https://www.youtube.com/watch?v=sg-9LuCQXrk

Easy!

JELL-O Comb Over TV Commercial http://www.youtube.com/watch?v=gporNcuC76M