In Patagonia by Bruce Chatwin (1977). The classic English-language travel book about the region, a rambling and brilliantly written sequence of fragments stitched together as Chatwin chased rumours of bandits, Welsh settlers, and a piece of mylodon skin across the south. Half of it isn't even true. Still the best single book on the spirit of Patagonia.
The Old Patagonian Express by Paul Theroux (1979). Theroux travelled overland from Boston to Esquel — south of Bariloche — by train and bus, ending his journey on the narrow-gauge La Trochita that still runs out of Esquel today. Gives a sense of how isolated the region was within living memory.
Idle Days in Patagonia by W. H. Hudson (1893). The Anglo-Argentine naturalist's account of an unplanned year on the Río Negro after a shooting accident left him stranded. Patient and observant, with descriptions of the steppe birds and people that still hold up.
El Pasajero del Tren del Fin del Mundo by Adolfo Bioy Casares — a slim Argentine novel about a doomed train journey, set in the wider Patagonian imagination that Bariloche helped create. Available in English as The Russian Doll.