This is my current laptop wallpaper:
It probably says how excited I am for the game (coming out this friday!). Usually though, my wallpaper isn't that. And it usually takes me forever to pick one. My wallpapers usually consist of a topic I'm interested in (anime, video games, or other). And I usually pick one that doesn't have a central focus on the image itself, doesn't include straight lines, but is still visually interesting. It takes forever to find one that I like.
I used this one for a long time:
And this one was the first one I used on my new laptop:
But yea, usually my wallpapers consist of whatever I'm interested in (either at the moment or in general). So that usually involves the Zelda series, or some anime series I enjoyed. I've had some non-zelda/anime wallpapers as well, but they are few and far between :P