The Roots of the City.  Mexico City's evolution.
http://www.mexicocity.com.mx/history1.html

The Tramways of Mexico.  This well-designed site tells the story of street railways in Mexico City and numerous other cities in Mexico.  Excellent maps, photos, and historical descriptions are included.  The photos and maps tell us as much about the historic urban landscape as they do about trolleys.  By Allen Morrison.  [ccr]
http://www.tramz.com/mx/tto.html