I was poking around and found some more about:* pages. A few, actually. Enjoy.

about:memory

about:stats

about:network

about:internets

about:histograms

about:dns

about:cache

about:plugins

about:version

I found references to two more, but they don't appear to do anything. Maybe they are for a special internal debug build only? Anyway, they are:

about:objects

about:chrome-nativeui