Into Thin Air by Jon Krakauer (1997) — the definitive account of the 1996 Everest disaster. If you're heading to the Khumbu, read this before you go. Vivid, honest, and unflinching about the commercialisation of Everest climbing.
Into the Silence: The Great War, Mallory and the Conquest of Everest by Wade Davis (2011) — the best book written about the early Everest expeditions. Dense but magnificent.
The Snow Leopard by Peter Matthiessen (1978) — a spiritual journey through the Dolpo region of western Nepal. A classic of travel literature, though the landscape it describes is still mostly inaccessible.
Arresting God in Kathmandu by Samrat Upadhyay (2001) — short stories by Nepal's first English-language fiction writer to be published in the West. A useful window into middle-class Kathmandu life.
Forget Kathmandu by Manjushree Thapa (2005) — a political essay and memoir about Nepal's Maoist insurgency and the royal massacre of 2001. Essential reading for understanding modern Nepal.
The Inheritance of Loss by Kiran Desai (2006) — not set in Nepal but partly in the Darjeeling hills near the Nepal border. Touches on Gurkha politics and gives context for the ethnic dynamics of the eastern Himalaya.
Tiger for Breakfast by Michel Peissel (1966) — the biography of Boris Lissanevitch, the Russian émigré who opened Kathmandu's first hotel and bar and essentially created Nepalese tourism. Reads like fiction.
Trekking in the Nepal Himalaya (Lonely Planet) — the standard reference for trekking route planning. Updated periodically; check for the most recent edition before your trip.