might be the only one right now who uses a dark power for good intentions. He fights fire with fire.
should have a place too, since he's been affected by the void, and unless there are any further retcons, he's lived for hundreds of years. Last time we saw him, he was looking for champions strong enough to fight against the void.
isn't an evil character, but it's hard to tell to what extent she's using her powers for good. So far for her it was all about survival. Given the nature of her suit, it's hard to tell if she can do any good at all, without being consumed by the parasite in the process. Constantly searching for food for the suit, while also saving the world might be a problem.
depends on how you see her. She punishes oathbreakers and betrayers, so she should be considered a good spirit. Or a rightful one at least. That said, she embodies the concept of "an eye for an eye", given her punishment is always death, which should sit too comfortably with our morals. By that I mean the concept of justice in the real world in 2015. Morally grey is more fitting.
. Runes aren't outright evil like the void, but should still be considered a dark power. Thus Ryze could join Kassadin in the group of heroes who use dark powers.
Swain too is a good candidate: the demon he controls is totally evil, and he plans to use it in a war against an evil force. So we can only say that fights for good intentions. Still he's more morally grey than Ryze and Kassadin, in that he's also concerned about building Noxus into a nation of strength, and for that he invaded Ionia and is constantly at war with Demacia.
hunts criminals in Zaun. He was horribly tortured and mutated by singed, becoming the monstrosity we all know and love. But now he fights for good. He should be considered a good guy. He just hasn't powers strong enough to save the world, so he's content with keeping Zaun's streets as clean as he can.
should count? He was created in order to be used as a weapon, only the guys tasked with nurturing him decided to raise him for good. So now he's a good guy, but his powers, and whatever he is, wasn sorta evil in the first place.
depends on how you see him. He's my favorite character, but I wouldn't consider him good. Many times he says that the only way to save the world is to let it die. He wants to defeat Mordekaiser and destroy the mist, which is good. But it does it in order to let the world die its final death, so if he ever does defeat Morde, he'll start an end of the world of his own making. Which is not good. He can be considered good as far as his mission hasn't been completed, then he'll be a menace for every living being in runeterra. Basically Aatrox before new Aatrox arrived.
is considered evil but think about it: he only wanted to end monarchy in Shurima. Is that a bad thing? Sure Azir wanted to end slavery, but it's not like it was his first decree, it was more like "I'm gonna be an immortal demi-god, you guys can do whatever you want now, I don't care, as long as I'm still a pharaoh". It's safe to say that after hundreds of years of imprisonment his mind as at least partially snapped. But he's actively trying to destroy the world. Then again, we don't know if he'll ever put his power in the service of good, but I say that it's still possible.