Recently I've become obsessed with an illustrator named John Harris. I'm about four or five decades behind the times, because he's one of the most respected sci-fi (and sci-fi book cover) artists working. I have no doubt I'd seen his work before - and I know I have, in fact, because I own a paperback of Scalzi's Old Man's War - but for some reason it didn't stick with me until Mike Brooks's novel Dark Run (I can never remember the rules for that name ending with "s" thing).
Mr. Harris has since graced my phone background for the last month or so, and eventually I moved into the wider sci-fi book cover genre looking for cool images. I change my wallpaper pretty regularly, and use it as a means of inspiration - this last part was kind of a shock to realize, which happened, legitimately, as I was typing the first sentence in this paragraph.
While searching for more John Harris art I came across a site that is now a regular stop. It's called Graphicine, and it's a fantastic library of visual inspiration. I've included some of the stuff that leapt out at me, but you need to definitely check the site out yourself. There's a lot of awesome reference and inspiration.