Get this Digital Clock Wallpaper, which is always showing the current time. You can activate or deactivate the seconds in the settings of the wallpaper.
Note: It is live wallpaper so you can't open the app, you will need to follow the instruction in order to set the wallpaper.
Instruction:
Home -> Menu -> Wallpapers -> Live Wallpapers
This wallpaper is completely free and without advertisement!