A little while ago, I came across "The Shape of the Nightmare to Come" by LordLuccan on the "heresy online" forums.
Since Games Workshop won't be advancing the Warhammer 40k storyline at any point in the next several years, various readers have remarked that this fits very neatly as a substitute.
The writing represents some of the finest Warhammer 40k fanfiction that has ever been posted to the Internet.
So, as a way to express my gratitude to LordLuccan and also contribute to 1d4chan...
And because I was absolutely marvelled by the writing and can't stand the thought of it falling off the web (since it was posted to a forum, after all)...
I've compiled its various sections, wikified the works (and this took a LOT of time and energy! SERIOUSLY!!), enhanced the navigationability of the chapters, and have posted them to 1d4chan.org .
I'm sure you'll love it. Enjoy.
(this is the 'title banner' for those of you who can't see the off-site graphic automatically)