These files have all been resized to fit as wallpaper for an iPhone (480 pixels by 320 pixels). There are all images downloaded from Spaceflight Gallery located at the NASA site.
These are the images I’d like to have on my phone. Hopefully you’ll find some that you like as well.
To download just click on the image to open the iPhone version. Then control-click (Mac) or right click (Mac or PC) and choose “Download”.