I am a total sucker for good editing and good transitions, even in commercials. The first great example of this -- and still my favorite -- that I can recall is the Nike "Move" ad from 2002. There are two recent ads that have also caught my eye:
This Stanley Cup ad is neat, if on the choppy side:
And this camera ad is a great mix of photography and film:
It's almost enough for me to reconsider my opposition to Flickr adding video.
What other brilliantly edited sequences -- from ads, movies, whatever -- do you love?