Book of Five Rings
The Classic masterpiece by Miyamoto Musashi.
The Celestial Agonies
L5R RPG Blog that is no longer updated, but still has a number of interesting posts.
Kaze no Shiro
Archive of most of the fiction–fanmade and canon–related to Rokugan.
Legend of the Five Rings Character Manager
A nascent .exe like the DDI Character builder, only for L5R 4ed. (Read Review)
Legend of the Five Rings Wikia
It’s like a searchable index to the published supplements, with a lot of info from the out of print Way and Secrets books.
Musha Shugyo
High-quality fanzines free for download, the issues cover such topics as the Imperials, Minor Clans, Non-Humans and the Shadowlands with an exception eye for detail.
Official AEG Forums
The primary resource for local groups, events, discussion, etc.
Shades of Honor
Seemingly the most in-depth and coordinated online play-by-post game running right now.
Writable 4th Edition Character Sheets in .docx format
An alternative to PDF’s.