What resources are available, including both free articles/ebooks and physical books and things, for game developers looking to begin simple AI programming/design?
Note: I know of this question, but that's more asking about where to start on a specific topic; I'm more asking about resources in general.
Programming Game AI By Example by Mat Buckland is an excellent resource to get started. He starts right from the basics of state machines and moves on to steering behaviours and graph theory for pathfinding. Probably one of the best resources I've found, especially when starting out.
The AI Game Wisdom books are also very good, but a lot of the articles are pretty advanced.
A good link for steering behaviours is this site: http://www.red3d.com/cwr/steer/
And as has been mentioned, http://aigamedev.com has amazing content, right from the frontlines.
Amit's Game Programming site is pretty decent at getting an overview (although admittedly, I haven't used it much): http://www-cs-students.stanford.edu/~amitp/gameprog.html#ai
I'd thoroughly recommended Buckland's book though. Very easy to follow and the source code actually works :)
Ray
I'm a really big fan of this book in terms of 'simple',
You can find it for about $5.00 on Amazon if you factor in shipping from a 3rd party. It talks about basics and good material for tile based games, which are great starting points for developing.
Half their content is behind a paywall, and it's practically impossible to find anything specific (like if you're trying to find their articles on behavior trees), but the content is second to none.