Nose comes with a handy option to generate profiling stats.

To profile your code, create a test dedicated to this purpose and run it with the right options:
$ nosetests --with-profile --profile-stats-file stats.pf test_performance

This will run the tests that corresponds to the test_performance name and generate a stats.pf file.

Nose uses hotshot, so if you want to generate a file that can be read directly by the pstats module and all the statistics tools out there, you need to convert it using the hotshot.stats module.

From there, there is plenty of tools that can transform such a file into a visual graph. Most of the time, they use Graphviz to render a graph, by generating a file dot can read. This software is most of the time easy to install through a binary distribution on your system. If you need to compile it... good luck.. ;)

Anyway, from there, I use gprof2dot, which renders a nice graph with meaningful colors.

From the author:

The color of the nodes and edges varies according to the total time % value. In the default temperature-like color-map, functions where most time is spent (hot-spots) are marked as saturated red, and functions where little time is spent are marked as dark blue.

If you want to use it, I have created some console scripts for conveniency, you can install using [easy_install][]:
$ easy_install pbp.scripts

It creates a gprof2dot script you can use, following the author documentation, but also a hotshot2dot script that will convert automatically a statistics file and pass it to gprof2dot:
$ hotshot2dot /path/to/my/hotshot/file

This will print in the output a dot file, you can send to the dot program, using a pipe:

$ hotshot2dot /path/to/my/hotshot/file | dot -Tpng -o output.png

You will get the visual result in output.png.