Beyond Good and Evil — Nietzsche's definitive critique of moral philosophy — complete text including all nine chapters and the closing poem. Helen Zimmern translation, 1906. Project Gutenberg EBook #4363.
Ecce Homo — Nietzsche's autobiography, written in 1888 on the edge of his breakdown — a fierce, self-aware summing up of his life, his works, and his destiny, concluding with the famous declaration: Dionysus versus Christ.
The Gay Science — Nietzsche's joyful philosophy of convalescence and the open sea — complete text including the Preface, the 63-poem prelude Jest, Ruse and Revenge, all five Books, and the Appendix Songs of Prince Free-as-a-Bird.
The Twilight of the Idols — Nietzsche's compressed philosophical masterwork — a hammer-blow survey of Western philosophy and morality: the problem of Socrates, the death of the true world, the spiritualisation of passion, and the eternal Yes to life.
Thus Spake Zarathustra — Nietzsche's masterwork in four parts: Zarathustra descends from the mountains to announce the death of God, the Superman, and eternal recurrence — in Thomas Common's 1909 translation.