Slytherin are ambitious, and / or very proud, and, of the classic Legion, Shady seems to fit that pretty well, and perhaps Dawnstar, as well. Karate Kid / Val might be an unusual case here, as well, as he was extremely proud of his own abilities, although lacking the sinister ambitions of his father.
Griffindor are kind of idealistic good-guys, defined by their courage and (occasionally) bull-headedness, which makes me think of Rokk and Superboy and Phantom Girl, heavy on the idealism, and Brin and Drake and Salu, a bit more of the 'monkeys that run *towards* danger.' Lightning Lad, definitely. It doesn't hurt that Griffondor pretty much has 'superhero house' tattooed on it's ass.
Hufflepuff are odd guys out, not really famous for anything else, which suits Colossal Boy, and yeah, Chuck. Possibly Sun Boy, as well. He's got the rich family / bloodline to be Slytherin, the brains to be Ravenclaw and perhaps the heart to be Griffondor, but sometimes comes off as too unmotivated to earn a place in either of those three houses, and content to just go with the flow.
Ravenclaw are brilliant, and rarely shy about letting you know about it, and yeah, Brainy's totally Ravenclaw. (Lots of Legionnaires are bright, like Dreamy and Cham and Imra and Lyle, but most of them are pretty laid-back about it.)