Wallpaper that has a basic grid pattern, like graph paper, would be really great for those of us who lean in the direction of OCD, making it much easier to line stuff up exactly as we'd like it. It's not something I'd leave up, but would love to be able to use it while moving objects in my home.
Some of the existing wallpaper helps somewhat, but a true grid (or even checkerboard, or plaid, or such) would be even better.