The Shore Excursions give you a good deion of what you can do at each port.
For us if we are going to do this trip, we would spend a few days Pre-cruise at Santiago, and spend a good deal of time Post-cruise at Buenos Aires/Argentina, and would most likely make a trip to Iguazu Falls.
http://en.wikipedia.org/wiki/Iguazu_Falls
Note the reported comments made by First Lady Eleanor Roosevelt "Poor Niagara!". :)
See the link for pictures.
http://images.google.com/images?q=iguazu+falls&hl=en&lr=&rls=GGLD,GGLD:2003-37,GGLD:en&sa=X&oi=images&ct=title
http://www.greatestplaces.org/book_pages/iguazu2.htm
Hope you enjoy seeing those pix.