As a test, try to set your backend to either 'cocoaagg' or 'macosx' like so:
import matplotlib as mpl
There have been issues with TkAgg on macs. I have personally not had any success with it (even with ActiveState's Tcl).
tried doing the above but this required me to install something called PyObjC:
The CococaAgg backend required PyObjC to be installed!
(currently testing v1.3.7)
when I tried to easy_install PyObjC it gave me the following error:
Unknown distribution option: 'use_2to3'
error: Could not find required distribution pyobjc-core
I am sorry for this but I easy_install-ed pyobjc-core, and then easy_install-ed PyObjC.
Now the pyplot.show() command works.
My matplotlib is now up and working!
Thank you, (esp ben.root)