[Beanamir of Gondor]

Your question is somewhat confusing, but I think I've worked it out: Tolkien certainly personifies the Ultimate Evil, i.e. evil deeds performed with no end other than the dominion of evil itself, in Morgoth and Sauron. Yet nowhere does he singly personify the Ultimate Good, i.e. good deeds performed with no end other than the dominion of good itself. Even with no ulterior motive, no single character devotes their entirety to the destruction of evil: they grieve for each other's deaths, they hesitate and make mistakes...

I would argue (rather simplistically) that while the Professor channeled "evil" into one or two characters, he spread the "good" out through the races, into multiple characters with seperate functions. We see some goodness in the Noldor as much as in the Riders of Rohan. Why? My still-simple argument would be that while absolute evil is easy to believe in, there's a tendency in society, at least ours, to reject the totally good as unbelievable. Melian comes close, but we are distanced from her as not to know how close. Perhaps the Professor just didn't want to personify God in his fictional works: you did mention that he was a Christian.

I can see your frustration at this, because I myself am feeling it in trying to explain my own feelings. Are we left with one Ultimate Evil, and a huge array of middling Good-But-Weak characters, and no Great Good? I hate to cite Harry Potter at a time like this, but the world isn't split between good guys and Death Eaters. There are so many inbetweens like Maedhros and Thingol, who are on the whole meant to be great and good but somehow fall spectacularly; who are neither Valar nor Morgoth's servants. Also, I will certainly cede that Iluvatar seems to be a laid-back sort of Creator, creating and then sitting back to watch, but does that mean he is not a Great Good? If Tolkien was a Christian, the destruction of Beleriand can be no more evil than the Great Flood (of Noah), and Eru therefore no less of the Great Good than the Christian God.

My greater question would be whether or not Good means Perfection. Can you still be Good if you make mistakes, or have weaknesses? I certainly wouldn't consider Boromir to be the Ultimate Good in the books, but he was only flawed, not evil. And if you had to classify him, he would have been wholeheartedly on the side of Good: only the presence of ultimate evil led him astray.

[edit] P.S. If this thread is meant to be argued in context of Tolkien's beliefs, I'll quietly withdraw... but for now I just hope I didn't do more confusion than good.