Picked this one up at our local bookstore, seems well written and reasonable to understand. I looked at it in the store for several weeks before buying it. I would imagine around here, books on this subject would not move off the shelf too quickly.
To my surprise, after I bought my copy, another showed up on the shelf next time we went. Goes into alot of detail with steering behavior, pathfinding, decision tree, history, flocking behavior,.....
http://www.amazon.com/Artificial-Intelligence-Kaufmann-Interactive-Technology/dp/0124977820
