The Discordian holy text by Greg Hill (Malaclypse the Younger) and Kerry Thornley (Lord Omar Khayyam Ravenhurst), with a foreword by Robert Anton Wilson in later editions. Not chaos magic proper but essential context. Most chaos magicians have read it; many were radicalized by it.
Chaos Current / Adjacent
Adjacent
Currents next door: Discordianism, postmodern occultism, cousins
Hakim Bey's 1991 manifesto on ontological anarchism and fleeting zones of autonomy. Not magic, but adjacent. Near universal reading in the 90s and early 2000s chaos magic scene; its fingerprints are on much of the practice that followed.