Articles
Working facial animation for custom models -- (forum topic)
Unknowns - Stuff that doesn't have a good explanation...yet.
Source Eyes: Taking a closer look - "Bottom line is [create] flat planes [for the eyeballs]."
Shading a Bigger, Better Sequel - Techniques in Left 4 Dead 2 (by Bronwen Grimes, Valve) (From: Valve Publications)