Is he really considered a villain though? I'm not very educated in LOTR, but isn't he only bad because he's being controlled?
Then again, I might have it all wrong >.>
Anyway, I really liked Light from Death Note.
Much like how the death note corrupted Light into becoming a villain (though Light probably wasn't very stable to begin with, and the power got to his head), the ring corrupted Sméagol and he murdered his relative when he refused to give it to him. Though Sméagol was corrupted immediately while Light got in way over his head after a few successful killings, but both had pitiful--but karmic--deaths. Funny how similar the two are.