Thanks to amk, PyPI now has a browsing feature. This has been developed along the lines of the Flamenco Search Interface Project (hey, look, another of Ping's projects ;)
The rapidly expanding size and complexity of information collections necessitates new interfaces for exploring, searching, and understanding their contents. The Flamenco project investigates how to effectively incorporate large, faceted category hierarchies into information access user interfaces.
The result is really quite usable. I'll look into the formatting of the categories some time later maybe. Hopefully I can just do some CSS magic to format the category "boxes".
Oh, and remember that if you're interested in any of the PyPI code, you can just grab if from the project page.