Just a smooth no stress wallpaper. Almost the same like - [link]
but with a little bit more smoothness (less "jaggy") and darkness.
2560x1600 - Widescreen
480x800 - HTC Desire
320x480 - iPhoneTip: If you change the wallpaper hue (color) in Photoshop and notice that some jagginess appear you can apply a small radial blur > zoom to get rid of it.