WSGI Explorations in Python by Mike Orr
An Introduction to the Python Web Server Gateway Interface (WSGI) by Titus Brown
A Do-It-Yourself Framework by Ian Bicking
URL Parsing with WSGI by Ian Bicking
WSGI and WSGI Middleware is Easy by Ben Bangert
WSGI - Gateway or Glue by Mark Rees (particularly good as a starting point)
An Introduction to WSGI by Ian Bicking (slides, handout, and code examples)
Mix and match Web components with Python WSGI by Uche Ogbuji
1. 'Hello World' with WSGI, 2. WSGI Middleware by Rufus Pollock
Why so many Python web frameworks? by Joe Gregorio (outlines the creation of a web framework using several WSGI-based tools)
Introducing WSGI: Python's Secret Web Weapon by James Gardner (Published on xml.com Sept 2006. Part 1: Getting Started)
Introducing WSGI: Python's Secret Web Weapon, Part Two by James Gardner (Published on xml.com Oct 2006. Part 2: Making Use of Middleware)
Please add to this list any introductions to WSGI that you find on the web.