Part One of the History of Rokugan:

A history of Rokugan from the earliest dawn of time until the Scorpion Clan Coup.

A Gaijin's Guide to Rokugan, Part 1
A Gaijin's Guide to Rokugan, Part 2
L5R History: Prehistory (from Imperial Herald #14)
The Naga (from Imperial Herald #2)
Private lessons by David Thun

Dawn of the Empire

Booklet in Ten parts
Dawn of the Empire, Part One of Ten
The Daughter, Part Two of Ten
Glorious Battle, Part Three of Ten
The Perfect Gift, Part Four of Ten
The Hand of Peace, Part Five of Ten
Way of the Dragon, Part Six of Ten
Defenders of the Empire, Part Seven of Ten
Fires of the Phoenix, Part Eight of Ten
A Gathering of Thunder, Part Nine of Ten
Day of Thunder, Part Ten of Ten

Dawn of the Empire Card list and Flavor Text (contributed by Bayushi Hagane)

Imperial Herald v2 #13