A many years ago, a friend of mine leveled the criticism at the Lord of the Rings that lots and lots of people get corrupted (Saruman, Gollum, Denethor, Boromir, Lotho Sackville-Baggins, etc) but nobody ever gets redeemed. At the time I made some half-hearted response about Theoden and the idea that Boromir's redemption is Faramir, but it was fairly lame and didn't deal with the big issue, which is Gollum.
I realize the other day that the reason there aren't very many redemptive examples in Tolkien is because the underlying narrative isn't about redemption, it's about forgiveness.
This makes a whole lot of sense when taken in the Christian setting. Tolkien was not writing any kind of Christian allegory like Narnia, of course, but he built his world on Christian premises, including the following:
1) All things are created Good
2) The world is Fallen
In such a setting you can't really have bad guys who are redeemed. You can only have good guys who are corrupted - some of whom (eg Theoden) shake off that corruption and others of whom don't. But everyone started out as a good guy. Add to this the fact that (in a Christian setting) redemption is not something that people do, it's something that God does. All people are able to do is to forgive.
When you re-examine the various books in terms of forgiveness, suddenly the examples are everywhere. Yes, Boromir falls in a moment of weakness, but he is able to ask for (and receive) forgiveness from Aragorn. Lobelia Sackville-Baggins ends the feud by finally forgiving Frodo. In the very last act of the story, Frodo forgives Saruman. Earlier, when he's convinced they're about to die, he asks Sam to forgive Gollum (implying that he has already done so himself). For his own part, Gollum's ultimate fall in many ways hinges on the fact that he is never able to forgive the theft of the Ring, never able to let it go.
The two most important scenes in the Hobbit (morally speaking) are Bilbo's sparing of Gollum and Thorin's death. The first of these is an act of pity and, in particular, mercy - which is more than halfway to forgiveness anyway. And, of course, Thorin's dying act is to forgive Bilbo. They're building this up in a particularly big way in the movie, where practically the first words said about Thorin are "he never forgave." Does Bilbo do anything in particular to earn that forgiveness? Of course not - he slept through pretty much the whole intervening scene. That scene has everything to do with Thorin and practically nothing to do with Bilbo.
I realized something just this morning. A particular favorite piece of dialogue from the beginning of the Hobbit goes thusly (forgive my paraphrase errors)
"For your poor mother Belladonna Took's sake, I shall give you what you asked for."
"I beg your pardon!" said Bilbo. "I haven't asked for anything!"
"Yes you have - twice now. My pardon. I freely give it."
Yes, it's flippant, but Tolkien's biggest points often are. Bilbo's story begins and ends with him being forgiven by someone.