i'm going with the light sabre from star wars...
great visual and sound effects made it pretty believable, no one's ever really denied its authenticity.
ps, like i said in the original thread all the really great cgi shots go under our noses because we don't even realise they are cgi. True cgi is supposed to fool you, not make you think about how good the effects are.
we seem to come at it from the opposite end because the quality is not always up to scratch, anything that doesn't take you completely out of a film these days is considered decent.