[Azaelia of Willowbottom]

Boromir is one of the most tragic characters. He was tormented by the Ring the whole time he was on the quest, and as a result, was never completely trusted by other Fellowship members. He really did only want the best for Gondor, but in the end, he wasn't even able to help.
Denethor is also tragic. He started out as a very intelligent, noble man... but his tragic flaw was his pride. Because of this pride, he neglected his younger son and in the end was driven insane by Sauron. Once I got over my horror at what he was doing, I felt bad for him. He could have been great, but he was twisted into evil.
Frodo's story is also tragic. He set out with no real intention of going all the way to Mordor, but he did, and it destroyed him to the point that he couldn't live on Middle-earth any more. I found it incredibly sad that he set out with the goal of saving the Shire, but when he returned, he found it completely changed and ruined. Even after driving out the evil, he couldn't stay. He was ill frequently, and probably in pain a good deal of the time, due to the destruction of the Ring. In the end, he couldn't even enjoy the return to the way of life that he had set out to save. He was a hero, but sometimes that can have a huge, even tragic price.