As usual, the best place to start is Lonely Planet.
Trekking in the Central Andes is brilliant, but has not been updated since 2003.
Lonely Planet Patagonian Andes has been updated:
This vast, varied region is home to some of the world’s great treks, with trails that take you through pristine forests to the rims of glaciers, under granite monoliths and over rickety suspension bridges, well beyond the crowds. Our expert author has chosen the best of Patagonia’s trekking, from the luxuriant rainforests of the Lakes District to the spectacular wildernesses of Tierra del Fuego.
Trekking in the Patagonian Andes (updated November, 2009)
Val Pitkethly’s book was updated, as well, September, 2008.
26 treks and 18 climbing peaks in the Andes, with coverage of the range from Venezuela in the north to Patagonia in the south. The treks included will introduce you to all aspects of the Andes, from the simmering volcanoes of Chile and Argentina to the high altitude Inca cities of Peru. Ranging between four days and two weeks, there is something for everyone.
Leave a comment if you have other faves.
besthike.com 
Trekking and adventure tours in Ecuador and South America with PALMARVOYAGES
ECUADOR is the country of « biodiversity » and volcanoes therefore it is the country of the adventurers, sports people and nature lovers.
Its natural regions : the Andes, the Amazon, the Pacific Coast and the famous Galapagos Islands is ideal to practice all sort of sport activities to your taste:
* For the amateurs of outdoor and mountain activities : Climbing of the highest Ecuadorian volcanoes (such Cotopaxi of 19358 ft and Chimborazo of 20702 ft) or trekkings, horseriding or mountain-biking across the amazing Andean cordillera with more than forty volcanoes, more than ten lakes, hot springs …
* For bird and animal watchers and flora lovers: walks or canopy activity in a tropical cloud forest, close to Quito or in the middle of the Amazonian forets of Yasuni, Cuyabeno parks and of course in the Galapagos islands…, the paradise of animals or whale watching on the Pacific ocean…
* For the passionates of extreme nautic sports: rafting or kayaking going down crystal-clear rivers lost in the Andes as well in the Amazon region, surfing or scubadiving in the Pacific ocean, close to “isla de La Plata” or much better in Galapagos, favorite spots for divers.
http://www.palmarvoyages
ecuador@palmarvoyages.com