I just submitted a pull request to add a streamplot
function to plot the streamlines of a vector field. This implementation is a modified version of the streamplot function posted to the list by Tom Flannagan [1].
This PR isn’t complete, but I wanted to submit it in order to get comments. In particular:

I haven’t added the pyplot function, only the axes method. It looks like the pyplot function should be generated by some boiler plate code.

I’m not sure what the docstring conventions are (the code isn’t terribly consistent), so I just (moreorless) followed the numpy docs.

Some parameter that probably should be adjustable aren’t at the moment (e.g. max streamline length, some arrow properties).

I left the original copyright from Tom’s implementation, but I don’t know if the BSD license has anything to say about that.
I’m not totally familiar with the matplotlib architecture so I’m probably forgetting a number of things. Feedback appreciated.
Tony
[1] http://www.mailarchive.com/matplotlibusers@lists.sourceforge.net/msg20208.html