I think I found most of them looking for a new desktop wallpaper, one of the various chan's I think. Amazing what you can accrue over time on a hard drive and not account for, especially when you have a memory like a tea strainer.
Source images, and their creative inspiration are below.
Spoiler
Portal 2
Unknown
Warhammer 40k
Unknown
Unknown
Original/Unknown
Tengen Toppa Gurren Langann
Tron: Legacy