After my talk at Scipy on colormaps, it was suggested that some of the information about the matplotlib colormaps be added to the matplotlib documentation. So, I spent my time at the SciPy conference sprints working on just that. So, I am now an official contributor to matplotlib with a guide to colormaps!
The plots I like the most are of the lightness parameter of the matplotlib colormaps, shown below. Colormaps that are more natural for our brain to correctly interpret typically have monotonically increasing values of lightness, so in the matplotlib cases, the Sequential and Diverging colormaps tend to be the best (the diverging colormaps are meant to show deviation from a central critical point, leading to the dual behavior seen in the colormaps). For more information, see the matplotlib documentation or the talks/slides.