Hm. A:TLA possibly, but maybe just some seinen anime, e.g., Samurai 7 or Death Note. A touch more whimsical, or at least more brightly colored. There was some excellent character work in Hourou Musuda, and Monster (which I've just been watching the past couple of weeks) has very good expressions.

Now that I'm thinking about it, stylistically it might be best to follow Code Geass. Angular, stylized, colorful, sexy, no chibis anywhere.