Flask
My favourite way at the moment to quickly get light, relatively simple web applications off the Ground:
Flask is a microframework for Python based on Werkzeug, Jinja 2 and good intentions.
I used it to build the GivenGain for Causes Facebook application (hosted on Heroku) in less than a week, initial learning period included. At the moment I'm using it to build a small-scale RSVP/Gift Registry/Communications app for the wedding.
The thing that makes it a joy for me to use is that you can set up a dev environment by downloading and installing Python & Flask, and testing it with the built-in development server, all within a matter of minutes, on almost any platform. The excellent documentation doesn't hurt either.
I'll still use Django (or try something like Pyramid) for bigger projects, but Flask definitely has its own special little place in my toolbox.
