One of the easiest ways to customize your Mac and express your personality is by using desktop wallpaper other than the default images in OS X. Apple supplies some fantastic images, and if one of them grabs you, then by all means, use it on your desktop.
Screen shot courtesy of Coyote Moon Inc.
Just don't forget that you can use just about any image for your desktop. There are tons of images available online; you can also use one of your own photos (you may need to use an image editor to crop it to the proper size).
For more information about changing your desktop wallpaper, including how to set up multiple desktop images, take a look at: