Rules

NetEA Tournament Pack

The NetEA Tournament Pack goes back to the idea of a living rulebook when Epic was seeing active development from Games Workshop's Fanatic division. It contains:

The official Epic Armageddon game rules and all of the errata. All is stressed here as some errata are missing from the rulebook PDF that GW published.
The most up-to-date FAQ available, essentially an expanded version of the last FAQ published by Games Workshop. Each Q&A is a footnote in the appropriate section of the rules.
All of the NetEA approved army lists as well as any rule extensions and Q&A's that accompany them. NetEA approved army lists are tournament ready and balanced against one another using the Epic tournament game rules. These lists vary slightly (point-cost and unit-stat-wise) from the official lists due to community feedback.

Official Rules

In addition to the original printed forms of the rulebook and Swordwind supplement, Epic's official rules were made available for free by Games Workshop and occasionally updated with errata (the printed books were never updated). However these PDFs were removed when the website was updated in 2014. They can now be downloaded here. Here's a breakdown on what each PDF contains:

Epic Updated Rulebook Sections 1–4: The core rules for Epic Armageddon including special rules, and rules for war engines, aircraft and spacecraft. This updated version was published in 2009.
Epic Updated Rulebook Section 5: Datasheets for Space Marines, Imperial Guard, Imperial Navy, Titan Legion and Ork forces.
Epic Updated Rulebook Section 6: Epic Tournament Game army lists for Space Marines, Imperial Guard and Ork armies.
Epic Updated Rulebook Reference Sheets: A game reference sheet and unit reference sheets for Space Marines, Imperial Guard and Orks.
Swordwind Part 1: Datasheets for Eldar forces.
Swordwind Part 2: Datasheets for Siegemaster Imperial Guard and Feral Ork forces.
Swordwind Part 3: Background for the Baran War.
Swordwind Part 4: Epic Tournament Game army lists for Eldar, Siegemaster Imperial Guard and Feral Ork armies.
Swordwind Reference Sheets: Unit reference sheets for Biel-Tan Eldar, Baran Siegemasters and Feral Orks.
Epic Speed Freaks: Datasheets and an Epic Tournament Game army list for Speed Freak Orks.
Epic White Scars: Datasheets and an Epic Tournament Game army list for White Scar Space Marines.
Epic Black Legion: Datasheets and an Epic Tournament Game army list for Black Legion Chaos Space Marines.
Epic Lost and the Damned: Datasheets and an Epic Tournament Game army list for the Lost and the Damned.
Epic Errata: An errata for the printed rulebook. The errata document was published in 2008 and most (but not all) of the changes were included in the Epic Updated Rulebook sections above.
Epic FAQ: The last official FAQ that was put out by Games Workshop.