We Wish to Inform You That Tomorrow We Will Be Killed With Our Families by Philip Gourevitch (1998) is the essential account of the 1994 genocide — how it happened, why the world failed to act, and what Rwanda looked like in its aftermath. Unflinching and very well written.
A Sunday at the Pool in Kigali by Gil Courtemanche (2000) is a novel set in Kigali in the months before the genocide, based on real events. It captures the atmosphere of that period in a way that straight journalism cannot.
The Antelope's Strategy by Jean Hatzfeld (2009) is the third in his trilogy on the genocide, focusing on perpetrators and survivors attempting to live alongside each other in the same villages. The earlier volumes, Into the Quick of Life and Machete Season, are equally important.
Land of a Thousand Hills by Rosamond Halsey Carr (1999) is a memoir by an American woman who ran a flower farm in Rwanda for decades and stayed through the genocide. Warm and illuminating about life in colonial and post-colonial Rwanda.
Gorillas in the Mist by Dian Fossey (1983) remains the definitive account of mountain gorilla conservation and the years Fossey spent studying them in the Virunga volcanoes. Essential reading before a gorilla trek.