If you want to learn about some of the different (but consistant) patterns currently used to create viral videos, read this post now. The author, Mark Laurie, does an excellent job grouping some successful videos into different groups and offers his thoughts (not backed up by any form of statistical analysis but still excellent) on how to create videos that could eventually become viral.
A lot of videos are well known - from the Cadbury Gorilla to Smirnoff Tea Party - however there are a few gems worth checking out.
A few of my favorites:
Games in Life