My Wife and I are going through Mexico at the moment and are travelling down to the bottom on South America, The Guia Roji is the best map for Mexico, It shows most roads including off road. I would suggest a GPS, but it is not a necessity, we do not have one although in saying that we would get one now if it was easy to do so.
In mexico heading south to central and south america until Jan 06
Finished 09/04/06, Denver Colorado to Ushuaia and back to Santiago. 27000 miles two up on a 2005 F650GS Dakar