What we are thinking re: itinerary (subject to completely changing our minds)
October - Week 1-2: Costa Rica
November - Week 3-5: Peru (Cordillera Blanca)
November/December - Week 6-7: Bolivia
December - Week 8-10 - Chile (Atacama Desert, Torres del Paine)
December/January -Week 11-12 - Argentina (Aconcagua, Tierra del Fuego)
The Chile and Argentina parts might go back and forth, across the border a couple of times, as Aconcagua is located half way between Atacama and Torres del Paine. Also, we really liked Santiago when we visited in 2006 and I would be happy to spend a couple of days in the city. Santiago is a good starting point from which to get to Aconcagua.
In terms of Bolivia, good friends of ours are planning a trip to visit their family in Bolivia in November. We don't have their dates yet, but hope to meet up with them for a few days. Depending on timing that might reverse the Bolivia and Peru parts.