Data visualization in Python

[kj]

I'm looking for a good Python package for visualizing
scientific/statistical data.  (FWIW, the OS I'm interested in is
Mac OS X).

The users of this package will be experimental biologists with
little programming experience (but currently learning Python).

(I normally visualize data using R or Mathematica, but I don't want
to saddle these novices with the task of learning yet another
language.)

TIA!

kynn