Eat Pray Love by Elizabeth Gilbert (2006) is the book most responsible for Ubud's current tourist volumes. Whatever you think of the self-discovery memoir genre, it's worth reading before you arrive — the Ubud it describes, of medicine men and rice paddies and yogic healing, still exists alongside the wellness centres and specialty coffee shops that have grown up around it.
A House in Bali by Colin McPhee (1944) is the better book: the Canadian composer moved to Bali in the 1930s to study gamelan music, built a house near Ubud, and spent years immersed in Balinese music and village life. He writes beautifully about the gamelan tradition and about the particular character of Bali before mass tourism. Essential for anyone interested in Balinese music or the 1930s artistic community.
The Island of Bali by Miguel Covarrubias (1937) is the classic ethnographic account of Bali between the wars — the Mexican artist spent two years on the island and produced a comprehensive account of Balinese religion, art, music, agriculture and daily life. Still the best single-volume introduction to Balinese culture.