Are there any libraries available for AI?
Yup, check Angry Ant’s Path and Behave.
StureStone also made a pathfinder, his demo also includes some RTS AI code.
For more info on Path and Behave check out http://angryant.com/path.html and http://angryant.com/behave.html
Check Lies and Seductions code, which is downloadable at http://mlab.taik.fi/~plankosk/blog/?p=308. It is not a library, but contains NPC AI (e.g., A* wayfinding using NavMeshes, Texas Hold’em poker AI).