Very, Very, VERY rarely, circumstances
can be so special as to dwarf even the unusualness of promoting a
pawn to anything other than a queen.
This actually happened to me once; unfortunately, it was when I
was in high school (which, at the time of this writing, was about
23 years ago) and I don't remember what the special circumstances
What happened was, my opponent picked up his pawn, gave the board one
last once over to make sure his plan was correct, then plunked the
pawn down on the eighth rank and replaced it with
one of my pieces! IIRC, it was a knight.
This wasn't in a tournament or a rated game, so we just had a laugh
over whether it was technically legal or not (I still don't know).
But it was certainly an example of thinking outside the box.
 I may be totally making this up, but my only guess as to why
this was an amazingly clever move is that it may have prevented a
stalemate which would have been created if he promoted the pawn normally,
by giving me a piece to move when I otherwise would have had none.
 December 22, 2002 Thanks to ariels' prodding, I went and looked it up. FIDE rule 5.6(d) states
On reaching the last rank, a pawn must immediately be exchanged, as part of the same move, for either a queen, a rook, a bishop, or a knight, of the same colour as the pawn, at the player's choice and without taking into account the other pieces still remaining on the chessboard.
and hence, the move was illegal. But according to rule 8.1,
it's too late to do anything about it now :)