Travel and Natural History
Papua New Guinea by Rowan McKinnon (Lonely Planet) — the standard practical guide, updated periodically. Solid on logistics and region-by-region coverage.
The Coral Triangle by Lyndon DeVantier and Emre Turak — for divers, an authoritative account of the marine environment of the region surrounding PNG.
History
Into the Crocodile Nest by Benedict Allen — Allen's 1987 account of crossing the Sepik basin on foot, full of detail on village life and the physical demands of the lowland forest.
The Siege of Rabaul by Henry Sakaida — covers the Japanese occupation of New Britain during WWII and the battles around Rabaul.
The Pacific War by John Costello — places the Kokoda campaign and the battles in PNG waters into the broader context of the Pacific theatre.
Anthropology and Culture
Sex and Temperament in Three Primitive Societies by Margaret Mead — classic, controversial anthropological work that drew on fieldwork in PNG. Read it as a product of its time, not as settled fact.
Pigs for the Ancestors by Roy Rappaport — a study of ritual, ecology, and warfare among the Tsembaga Maring of the Highlands. Foundational reading for understanding how Highland societies worked before significant outside contact.
Black and White: The Papua New Guinea Journals by Sean Dorney — an Australian journalist's decades of experience covering PNG from independence onwards. Informed and honest about the country's political difficulties.