HD Wallpaper: Riesenrad in Wiesbaden
The wheel from Wiesbaden, Germany in a 4K picture that can be saved free under CC By-Sa license from Martin's courtesy and set from here as desktop backgrounds and lock screen phones.
Widescreen Desktop / Macbook: 2560x1600 (fits on: 1920x1200, 1680x1050, 1440x900)
Samsung Galaxy Tab & iPad: 2048x1536 (compatible with almost all tablets)
HTC, Samsung Galaxy & iPhone: 1080x1920 (compatible with many smartphones)