Teemo is by far the best split pusher in the game.
He covers his escape route in shrooms, clears the minions waves extremely quickly, his mobility is amazing.
He can sprint up a lane faster than most champions, clear the minions (especially with a Runan's Hurricane) extremely quickly, shroom around river and routes where his enemies will attack him via so he can notify their presence, go stealth until they go away and continue pushing, leaving the enemy thinking: The hell just happened?

His damage is also great.

nidalee, shen, shaco, teemo come to mind, but it can be anyone who meets a few basic criteria: fast lane clear, tanky, good escapes, and HAS TELEPORT.

it pains me whenever someone decides to split without teleport, because simply put the enemy team can and will initiate 5v4 against your team lategame, and if it is even close to an even game, they will come out on top, and goodluck out pushing the enemy team after they decimate your team. also, imo adc's should never split. the risk is just too high. clean waves on your side of the map but never overcommit. let your team protect you and carry the game.

EDIT: i would love to know why this is downvoted...please post so i can laugh my ass off at how retarded you are.

i find myself doing this with MF...but for me its more along the lines of base trading and not necessarily BD/Split push...when 5 enemies at mid on my base and im at top or bot at their base...seeing as the tower is the 5th person to help defend i can destroy the base pretty fast late game and enjoy when the team sends ONE person back to deal with me...cuz he is dead and then i still kill their base

AP Xin Zhao...

Shaco, Shen, I PERSONALLY like rengar for the ult to get away/heal with his W while running.

I really like to split push with Singed using teleport

Jax shreds towers like nobody's buisiness.

Nasus can slit push if he has a decent farm

Mundo with wits end + E. Mundo smash puny tower, although there are better split pushers like Shen and Master Yi.