Ooh, I've been investigating this lately, and I can't sleep. Here are some entries from my bookmarks:
* BART map, one minute per hexagon - http://transitmaps.tumblr.com/post/133579339455/lopato-bart-...
* Mapnificent, covering dozens of cities - http://www.mapnificent.net/
* OneBayArea, including housing prices - http://maps.planbayarea.org/travel_housing/