A History of Modern Indonesia by Adrian Vickers is the most readable single-volume introduction to how Indonesia came to be the country it is — the colonial period, independence, Suharto, and the reform era all covered with clarity. Essential background for anywhere in the archipelago, but especially useful given Makassar's complicated colonial history.
Lord Jim by Joseph Conrad draws on Conrad's own time as a sailor in Southeast Asian waters. Parts of the novel are set in the Makassar Strait and among the Bugis trading communities; the atmosphere, if not the exact geography, still resonates in the port city.
Lonely Planet Indonesia covers Makassar, Sulawesi, and the surrounding islands in practical detail. Not elegant reading, but useful for transport logistics, accommodation, and day-trip planning, particularly for the Spermonde archipelago and Tana Toraja.
Sea Nomads of Southeast Asia or similar works on Bugis and Makassarese maritime culture — ask at a bookshop in Makassar for current titles, as the local selection on Bugis seafaring history is often better than what is available abroad. The Bugis were among the most accomplished blue-water sailors in the world, and their story is told imperfectly in most general histories.