Well, maybe not a million, but a LOT. However, I think none as unique as Ian and the flute... which I think is "King".
AND... a caveat.. most of the 'unusual' instruments were NOT the main instrument used by various musicians but rather used for a particular song.
Does a harmonica count? Several musicians used a harmonica as their main instrument.
The most unusual, but you probably won't count this...was June Kuramoto from the band Hiroshima, (semi-pop music), who plays a KOTO. I have never even seen or heard of another human being that plays a Koto.