Isbister's Character Design

Both Gamasutra and Dr Dobbs have excerpts from Katherine Isbister's book Better Game Characters By Design A Psychological Approach.

There's also more of her work availalbe online at Friendly Media, and her blog, Game Empathy.

Of particular interest is Noah Schaffer's Heuristics for Usability in Games white paper in which he presents a set of heuristics for game design.

Also her presentation, Perform or Else! and footage about "extroverted play design".

Isbister, Katherine. Better Game Characters By Design A Psychological Approach. (Morgan Kaufmann, 2006)