Help running matplotlib on Mac OS X

I'm trying to quit Matlab and use python fro my data analysis. I have installed the latest MacPython (universal), wxpython, aggdraw and matplotlib from Everything seems to work, apart from matplotlib. Running from ipython:

In [1]: from pylab import *
In [2]: plot([1,2,3,4])

I get:

Out[2]: [<matplotlib.lines.Line2D instance at 0x4ddfb70>]

but nothing appears, not even an error message. I get a bouncing anvil (MacPython logo) on the dock but nothing happens.
If I run python in verbose mode I get:

import MacOS # dynamically loaded from /Library/Frameworks/Python.framework/Versions/2.4/lib/python2.4/lib-dynload/
[<matplotlib.lines.Line2D instance at 0x4c9eaa8>]

unfortunately this means nothing to me. Can anyone help? Thanks,