"If it exists, there is porn of it."
Rule 34: There is porn of it. Yes, even of that. No, you don't want to think about this for too long. Even your mom, trust me. It goes without saying that Warhammer 40,000 is, like all things, completely subject to the many creative variations of Rule 34 that the Internet can conjure. It also goes without saying that the contents of this page (actually, the contents of many pages around here) are rather NSFW. Ironically, /tg/ is supposedly a safe-for-work board, but this isn't a guideline that is obeyed rigidly. On any day you can be browsing /tg/ when suddenly you get a faceful of Eldar porn, including some that might even be well-drawn.
On that note... don't read the article on FATAL.
Canonical Kroot porn.
Xeno vagina? Xeno vagina.
And what would Rule 34 be without our ever-loving space nuns, the Sisters of Battle? (Animated!)