I'd say the Operative from Serenity. He believes that he's working to create a better world, he supports law and order as an agent of the government, and he fully believes that his actions - even if it means killing people - are going to make the universe a better place. He has the humility to realize that those very actions make him unsuitable for the world he's trying to create, and he adheres to his code of ethics and honor as much as he can.
One could certainly argue that he's not LG - he himself would probably agree. He's a bit extreme in his pursuit of his goals... but he is pursuing those goals for the greater good (as he sees it). And when he finds out that he wasn't completely right about that greater good... he's able to change. Maybe his specific actions aren't paladin-y, but I'd say that his personality - his drive, his ethics and honor, his goal to create a better world - are all fitting for a Paladin.
One could certainly argue that he's not LG - he himself would probably agree. He's a bit extreme in his pursuit of his goals... but he is pursuing those goals for the greater good (as he sees it). And when he finds out that he wasn't completely right about that greater good... he's able to change. Maybe his specific actions aren't paladin-y, but I'd say that his personality - his drive, his ethics and honor, his goal to create a better world - are all fitting for a Paladin.