Flask is a micro framework for Python based on Werkzeug, Jinja 2 and good intentions.
Django is a free and open-source web framework, written in Python, which follows the model-view-template architectural pattern.
Scrapy is a Python framework for large scale web scraping programmes. It gives you all the tools you need to efficiently extract data from websites.
For teaching/learning programming. Focused on program runtime visualization. Provides stepping both in statements and expressions, no-hassle variables view, separate mode for explaining references etc.
Multi-language IDE with support for Python 2.x and Python 3. Available as Komodo IDE (commercial).
Commercial Eclipse-based IDE which provides a standalone bundling PyDev, Workspace Mechanic, Eclipse Color Theme, StartExplorer and Any Edit, along with lightweigth support for other languages, and other usability enhancements such as multi-caret-edition).
Python/Jython support in NetBeans -- Open source, allows Python and Jython Editing, code-completion, debugger, refactoring, templates, syntax analysis, etc.; see also http://wiki.netbeans.org/Python. UPDATE: Netbeans 7.0 released without Python support.
Python is free to use and distribute, even for commercial use as well as you can even make changes to the Python's source code. It has a large community constantly improving it in each iteration.
Easily move python programs from one platform to another, and run it without any changes. It runs seamlessly on almost all platforms including Windows, Mac OS X and Linux.
For high performance applications you can easily combine pieces of C/C++ or other languages with Python code. This will give your application scripting capabilities which other languages may not provide out of the box.
Python code automatically converts your code to the language of your computer. You don't need to worry about any lower-level operations like memory management, garbage collection and so on.
Everything in Python is an object. Object oriented programming (OOP) helps you solve a complex problem intuitively.
Python has a number of standard libraries which makes life of a programmer much easier since you don't have to write all the code yourself.