[Rosa Underhill]

The evil in Middle-earth is much the evil in our own world. Those who are truely corrupted can never submit to being forgiven; they may think themselves weak for it or simply not realize that they have such an option. Look at Hitler (who reminds me a lot of Sauron).

I don't think Gollum was himself after so long with the Ring. In fact, he wasn't. Gandalf said something about Gollum's mind and will being consumed by the Ring until there was nothing left but desire for it. I wonder what would have happened if Gollum hadn't been destroyed with the Ring. I think he probably would have died anyway, but it would have been worse for him. Illuvatar was merciful in sending Gollum into the Cracks of Doom with his "precious".

Boromir, however, was not truely corrupted. He repented after he tried to take the Ring and gave his life for Merry and Pippin as an act of redemtion (in my mind, anyway).

And some evil is just evil through and through. Smaug was too greedy to ever be good; he gave his heart to his horde, as is a dragon's want. And Sauron, well, we know about Sauron. A general in Middle-earth's version of Satan's army just doesn't turn back to the light. Ever.

Saruman was corrupted by greed, the same as Smaug. In the early stages, his craving for power could have been stopped, but he held onto it for too long and it destroyed him from the inside out. The same had happened to Wormtongue, though he might have always been coniving.

And it was the Ring's fault that Frodo turned. Once it was gone, he was closer to the old Frodo again. Though not the same as before he'd possesed it, his heart was still esentially good. (If the hearts of men can be good... But that's another matter entirely.)