I just released 0.9.1 of the Fudge module which is a tool for working with fake objects while testing Python code. Some call these mocks, stubs, or actors, but I just call them all fakes because that way you don't have to change the names in code if you update your tests. You can get Fudge from PyPI or by running easy_install -U fudge. This release contains some nice new features and several contributions by Cristian Esquivias. It has more documentation and some bug fixes but note that some functions have been deprecated.
See the changelog for all new features and details on the deprecations. Big thanks to Cristian for his contributions. Also, thanks goes to Marius Gedminas whose comments on my original Fudge announcement led to better names for some commonly used functions.
There is also an experimental, partially-implemented JavaScript port if you feel adventurous.