Technically this isn't "fan art" because I just stumbled across these illustrations, but it is an art-related thread that I hope will spark some inspiration for other fan artists and just plant some seeds of imagination.
So the following pictures are made by Ayami Kojima for the video game classic "Castlevania: Symphony of the Night", and I found them here:
castlevania.armster.org/scans_sotn.php
Please note that I DID NOT DRAW THESE PICTURES, THE EXTREMELY TALENTED AYAMI KOJIMA DID. I ONLY FOUND THEM AND THOUGHT THAT YOU MIGHT LIKE THEM.
Here are a few (I sized them down to fit the thread, they are of higher resolution on the website I linked to):
Seriously, these simply SCREAM of Rogue Trader to me. All that's missing are a few bolters, some bionics and perhaps some big shoulder pads. But aside from some of the vampiric imagery, the clothes, the hairstyles and everything just drips of pure Rogue Trader. I can easily see some of these characters roaming about the bridge of one of the "flying cathedrals" that humans call starships in the 41st millenium.