Jungle Tristana, she has some of the scariest ganks in the game. her rocket jump has the ganking power of Zac's jump since you can come from off screen, except there's no windup time. Once you hit 6 they get even scarier, now you can knock enemies back like a mile for a sure kill.
Jungle annie, e makes clearing pretty easy, and you have a 1.75 second stun to gank with.
I used to play jungle nasus before he was considered a jungler(people thought it was a troll pick), but then he started seeing competitive play :/ so I guess ti isn't unconventional anymore
Jungle Karthus, gank all 3 lanes at once(JK don't do this LOL)