The Upanishads

 Upanishads, Part One (SBE 1)
 Upanishads, Part Two (SBE 15)

The Sacred Books of the East started off with the Max Müller translation of the Upanishads; complete e-texts of these key works are available here. This edition contains a dozen of the most important Upanishads, which are fundamental texts of Hinduism.