While pondering my reference library.
Some books served to comprehensively define a previously invisible topic, and are still so dominant in their subject that they can serve as canonical. Three I can think of are K & R's White Book, Refactoring by Martin Fowler, and Design Patterns by the Gang of Four. What other books fall into the category of being generally considered necessary and sufficient for a major subject?
EDIT:
Try to avoid generally "good books" - which ones served to first define a subject, and still serve as an undisputed authority?