Zak has come up with a really cool variant for a Barbarian class. Basically, every time you level, you roll on a random table to see what you get. No just getting a +1 to hit every level (unless you keep rolling that). I think it's a really neat idea.
I would love it if someone actually made tables like these for every class, and published them. I'd buy it. It's actually the kind of thing I think would warrant a new OSR game. If every single class in the game has a random table needed to level (and maybe even at character generation), it would be a really cool twist to basic D&D.