Wasn't too sure about this one at first because he's on the cusp.
The last thing in the world Charlie wants is power, or to lead. He wouldn't last a day in Slytherin.
Charlie is too afraid of his own powers to really embrace it in the way needed to be the kind of hero Gryffindor calls for. While he'd save people in an emergency, he doesn't seek them out or believe in himself as a knight in shining armor.
He's definitely a studious type, concerned with learning and literature, but he's more community-minded than the more individualistic Ravenclaws.
Charlie probably belongs in Hufflepuff. He wants to make others happy, even to the point of changing himself and how he acts around them. He'll do for others at the drop of a hat, and has the determination and patience to toil behind the scenes for years, rather than seek any attention for himself. His defining trait is his attitude toward others.
The Scarf of Sexual Preference says: A Total Mindfuck