Idk, I kinda like Rammus for ganking. You can roll in really fast and lock an enemy down, and if you time it right you don't really need to run because of dat shield and hopefully your teammate is competent enough to attack while they're locked.
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Eve is good at going in and out extremely quick while doing a ton of damage.
Olaf is also really good in this fashion. If you hit his Undertow, you have a super strong gank, especially with your true damage to add to the mix. If things go wrong, you have your ult and possibly Ghost to get away from it.
Evelynn - Innate invisibility, zero cost movement boost, has ridiculously both burst and sustain damage. Ganking level over 9000.
Lee Sin - A gap closer, aoe slow, massive life steal and spell vamp, together with decent shielding ability. Quite good for a blind guy.
Twisted Fate - An almost-global sight and teleport, stun, slow, with a nice mixture of burst and sustain damage. Not to mention the additional gold he gives.
Amumu & Malphite - Two of the best initiators in the game. Tanky, chockful of cc, got abilities that are simply game-changing. Once they gank, it's an almost guarantee that at least an enemy will wind up dead.