Tkinter By Example
If you're looking to learn how to create GUI applications in python, the tkinter module is a great place to start. It's free, available in the standard library by default, and super easy to use.
I've written a free book which will walk you through creating 6 real GUI applications using tkinter - giving you everything you should need to begin writing your own applications easily.
This is a completely open-source book, complete with source code and other various assets for each project. Even the source of the book itself is provided should you wish to compile it yourself. Head on over to my github to download Tkinter By Example:
The book is licensed under Creative Commons Attribution-NoDerivs (CC BY-ND) . Please download, use and share it as you like!