I got a bit carried away with the explanations here (not to mention the video evidence) so I'm gonna tackle the other two Top 5's that beansidhe_baby asked me in a subsequent post. If you want to join in, leave me a comment and I'll try to think up some good ones for you too.
Top Five OTPs (I guess that should really be FTPs - "Five True Pairings?" Heh.)