I think he was Gryffindor. Neville isn't too bright, either.
Neville is brave and that is the quality Gryffindor valued most. He stood up to Harry, Hermione and Ron in Book 1 to keep them from sneaking out and getting into trouble. In Book 5, Neville fought Death Eaters while carrying the unconscious Hermione, despite his smashed face. In Book 6, Neville answered the call for help when Death Eaters invaded Hogwarts. He was one of only 2 DA members to do so.