Depends on how you define evil
For example, though Malzahar wants to pretty much end the world, I don't consider him evil, the entity inside of him exists to do nothing but consume, and Malzahar cannot fight it, as he was consumed.
Fiddlesticks is another entity, he just simply exists, he stands in a room all day and only harms those who enter, I wouldn't call him evil
Karthus isn't evil, if he was he would have sung Requiem and ended the world, he is a guardian, who likely has his own agenda and is waiting for some kind of trigger
Elise, Syndra, and Zen all fit the bill for evil, Syndra and Zen murdered their masters for power, Elise sold her soul to her 'spider god'
Veigar is also evil in his own little Saturday cartoon way, but he's insane, so once again I state, if one is not fully aware of their actions, if they're being controlled (as Malzahar is), are they TRULY evil?