Problem Solving with Algorithms and Data Structures using Python

by Brad Miller and David Ranum, Luther College (as remixed by Jeffrey Elkner)

CS Principles: Big Ideas in Programming

by Mark Guzdial and Barbara Ericson
Hands-on introductory computer programming using Python 3.

Beginning Python Programming for Aspiring Web Developers

by Jeffrey Elkner (with liberal borrowings from the work of Allen Downey, and Peter Wentworth)
An introductory computer programming text book using Python 3.

How to Think Like a Computer Scientist: Learning with Python

by Peter Wentworth, Jeffrey Elkner, Allen Downey, and Chris Meyers
An introductory computer science text book using Python.

Lessons in Electric Circuits

by Tony R. Kuphaldt
A free series of textbooks on the subjects of electricity and electronics