From Halopedia, the Halo wiki
Episode 1: The Unknown Helper (Adjutant Reflex posts • Forerunner Email • Halo 3: The Cradle of Life • Transmission Log • Society of the Ancients (Website))
Episode 2: Flood Control (Flood Containment Control)
Episode 3: Echoes Through Time (Halo3.com)
Episode 4: The Great Connection (When We Two Parted • The Castaway Theory • Amazon • Profvol49)
Episode 5: The Artifact (TheArtifactLocation.com)