The Philebus is a late Platonic dialogue on ethics in which Socrates argues against the hedonistic position propounded by his two interlocutors, Philebus and Protarchus.
Free online and downloadable texts
Gutenberg: Philebus, translated by Benjamin Jowett, multiple formats.
University of Adelaide (Internet Archive): Philebus, translated by Benjamin Jowett. EPUB, HTML and MOBI formats.
Wikisource: Philebus, translated by Benjamin Jowett (1892).
PhilPapers: Plato - Philebus - bibliography with open access option.
The Great Conversation: Further reading at Tom's Learning Notes
Ancient Greek resources: Learn to read Greek classics in the original.
Bloom's Western Canon: Plato's Dialogues are listed.