My opinion is Fruits Basket. It's got comedy, romance, and a little bit of action. I find it amazing because when I first saw it I thought, "Phfft, a girly anime." But I was hooked onto it. They made an anime that got my attention without extreme violence or hot anime girls.
Another is Fullmetal Alchemist. My opinion, it totally owns Harry Potter!! The average 6th grade non-anime kid only knows the word magic, and not alchemy. Very creative plot.