I've made a few space wallpapers using some of NASA's imagery. I will be posting the set of three over the next day or so. The first pair below are based on an image of the Tarantula Nebula found on the Hubble Space Telescope's website. If you click on that link you can even download the massive 32.1 MB original. There is some amazing detail in that original photograph.
iPhone 4 (click image for full resolution to use as wallpaper):