To install matplotlib on OS X Lion, the following tutorial did the trick for me.

I’m not sure about the state of homebrew by the time the tutorial was written, but right now even Qt can be installed via homebrew - unlike the according step in the tutorial:

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brew install qt

It even comes with QtConsole, nicely integrating your plots into the actual console:

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ipython qtconsole --pylab=inline

Background:

I have been using Python and its matplotlib extensively for a research paper I did in 2011. For me it combines the advantages of MATLAB with the power of Python without the insanity of gnuplot. It worked well on my Snow Leopard installation and integrated perfectly into LaTex. The thing is, I’m running Lion now and I switched from MacPorts to Homebrew (for sanity reasons). The downside is now that I can’t get matplotlib out-of-the-box anymore and straight forward attempts of compiling, easy_installing or piping failed so far (LLVM vs. gcc among other things).