One of my favourite's is the Rolo advert. The one where the young lad is watching a circus parade and teases the elephant with hs last Rolo. the next clip shows the lad as a grown man, again watching a circus parade and this elephant comes up and swipes him round the ear with his trunk.
I also like the Cadbury Smash adverts with the aliens. You know the one - they boil the potatoes for 20 of their minutes then they smash them all to pieces.
