Something I'm surprised hasn't made it's way into the discussion... "Alice's Restaurant Massacree" by Arlo Guthrie. Probably the most well known version of a song where the intro is better known (and considerably longer) than the song.

I've had this discussion in the past, and part of the resolution is that almost every song you do is going to have some sort of "introduction", even if it's no more than the body language you assume before performing it, or the banter between you and your 'mates. Unless you're mechanically moving from tune to tune, that is.

M