Chaco is a platform independent plotting library for Python developed by Enthought, Inc. for the Space Telescope Science Institute (STScI) and licensed under a BSD style open source license.
http://www.scipy.org/site_content/chaco
Chaco's goal is to produce presentation quality scientific 2D graphics on a variety of output devices. The initial targets are WxPython, TkInter, Mac OS X, and PDF for hard copy output.
Update
Update, looks like development has ceased. According to SciPy Version 0.3 Release Notes: BR Chaco development is occuring on a different source tree (svn://www.enthought.com/svn/enthought) and is no longer updated in SciPy.