Absolute Good in Lord of the Rings

[Tigerlily Gamgee]

I haven't had a chance to read all other responses... but for me, the answer would be Samwise Gamgee.

Why?

Samwise seemed to have a knack for "getting people" without really knowing them. He wasn't fooled by Gollum. He protected Frodo even when Frodo shunned him.
He was an all around "good guy."
He wasn't really affected by the Ring (granted, Hobbits in general were not as affected, and had he had it as long as Frodo it's quite possible he would've broken down too) when he took it, at least not to the point of failing on his mission.
He STUCK to his mission... his main goal was to see the Ring destroyed and Frodo home safely. He was kind of like a child in that he tried to remain untainted by everything that was going on.

Granted, this is from the movies, not the book, but I always loved this dialogue exchange, and I think they did an excellent job of writing Sam in the movies (for the most part):

Frodo: I can't do this, Sam.
Sam: I know. It's all wrong. By rights we shouldn't even be here. But we are. It's like in the great stories, Mr. Frodo. The ones that really mattered. Full of darkness and danger, they were. And sometimes you didn't want to know the end. Because how could the end be happy? How could the world go back to the way it was when so much bad had happened? But in the end, it's only a passing thing, this shadow. Even darkness must pass. A new day will come. And when the sun shines it will shine out the clearer. Those were the stories that stayed with you. That meant something, even if you were too small to understand why. But I think, Mr. Frodo, I do understand. I know now. Folk in those stories had lots of chances of turning back, only they didn't. They kept going. Because they were holding on to something.
Frodo: What are we holding onto, Sam?
Sam: That there's some good in this world, Mr. Frodo... and it's worth fighting for.