There are a lot of places to get backgrounds and screen wallpapers, so I'm going to bookmark my faves here.
If I want photo-style images, free stock photo sites can be great options. My favorites are:
The only problem with photos is that they can be distracting as backgrounds and can make it harder to see the various icons. But there are other options out there besides stock photos, for example this modern take on gradient-style backgrounds. For females, these girly backgrounds stay out of the way of the icons yet give an upbeat feminine look with soft colors.
I tend to prefer wallpapers which are in the red, pink, or orange hues because they're supposed to make it easier on the eyes late at night. I wish it were easier to find those colors of wallpaper in styles that don't conflict with or overwhelm icons. I need to find additional free stock photo sites as well, which might give me a bit more choice.