iOS: If you want to quickly turn any photo into an arty-looking blurred wallpaper which complements the iOS 7 design style, then Blur Studio is a really cool way to do it.
The app gives you a slider on any image to adjust the blur settings. You can also use another slider to adjust saturation. There's a neat little tray of colour filters to apply to the image, and a quick preview to see what it would look like behind your home screen. Fiddle around with the app and you'll soon get really cool-looking wallpapers for your iPhone with minimal effort.
The only shortcoming is that you have to save your creations to your camera roll, open up the photos app, and then apply it as wallpaper. There's no shortcut to reduce all those taps, which is inconvenient for an app that's all about creating wallpapers.