Gryffindor: Bravery, chivalry
Also boastfulness, pigheadedness

Ravenclaw: "Book smarts", a thirst for knowledge for its own sake

Slytherin: Ambition, cunning,
Also thuggery and contentment being a lackey as long as it gets you what you want

Huflepuff: The rest

A few examples to start off with....

Caius: Gryffindor. Proof that a Gryffindor can be evil. Devoted to his charge to the extent it would destroy the universe.

Ravenclaw: ???

Rinoa: Hufflepuff. Gentle, dedicated to helping others and very empathetic

Slytherin: Most villains but for a good Slytherin, how about Shadow or Amarant?