Here is nice ebook (a 74-page PDF file) about Python scripting for Blender 2.5x.
With the arrival of the Blender 2.5x versions of Blender, Python scripting is
taken to a new level. Whereas the Python API up to Blender 2.49 was quite
incomplete and ad hoc, the API in Blender 2.5x promises to allow for python
access to all Blender features, in a complete and systematic way. However, the learning curve for this amazing tool can be quite steep. The purpose of these notes is to simplify the learning process, by providing example scripts that illustrate various aspects of Python scripting in Blender.