Why not have a different one every day?
Mac OS X ships with some pretty fancy wallpaper options by default. You can also use your own wallpaper images using the System Preferences pane.
It’s nice to be able to have a different wallpaper every day. Here’s how you can set a rotation system for you Mac’s wallpapers so that your wallpaper changes at a frequency that you set.
Change Wallpaper Automatically in OS X
Click on the Apple logo at the top left corner of your screen and then select the System Preferences option.
In the System Preferences pane click on the Desktop & Screen Saver button.
Select the Desktop tab. Now you can pick an image folder from what is available to you by default, or you can add a new folder. Click on the + sign to add a new folder.
Once you have selected the folder from which you want the wallpapers to be picked, check the checkbox next to the Change picture option below the images. You can set the rotation time to what you want. You can set the interval from 5 seconds right up to once a day.