An apropos link from daringfireball today:
http://www.jordanm.co.uk/tinytype lists the available 'system fonts' on iOS/Android/Windows Phone/Blackberry.
For communication purposes, it would be great to fork it ( https://github.com/jordanmoore/tinytype) and add the available default system fonts on Mac OS, Window 7/8, Ubuntu, Red Hat, etc.
(Then the only missing piece would be the font-mapping information, so you could tell what font the string "serif" or "Helvetica" (say) is mapped to on the various platforms.) --scott