I recently created a few wallpapers which bear the signature “Designed by Apple in California”. They are extremely simple wallpapers, and you can download both of them by clicking the image thumbnail in this post.
I would like to give credit to http://www.myipodwallpaper.com for the grid wallpaper. I only added the “Designed by Apple in California” text.
Note: These are for personal use only.
Update: I’ve added three wallpapers (with a blue grid design) for iPhone 5, iPad with Retina display, and Mac (2560×1600). Blue background is courtesy of Louie Mantia.