The worst video I can think of off-hand is Van Halen's "Jump". I mean, here was a band pulling in multiple millions of dollars at the time, and they spent about twenty bucks on a completely black set and a camera, then filmed themselves in pseudo-concert.

Best video I've seen lately is Colplay's "Trouble", but discounting technical advances that just make the videos look better, I've a certain fondness for the Talking Heads' "Once In A Lifetime".