Personally, I keep it simple, aside from a custom wallpaper I unify the desktop appearance with UNO, which provides a clean and consistent interface to all of Mac OS X. I had no idea that Mac OS offers customization options until I started searching on this idea.
Customization comes in many forms, from the very simple changes to the screensaver or the Desktop background. You can convert the whole home screen from boring to attractive with just a few tools and docs. Today I am not featuring these tools because you can easily find them online. Today I have collected some great ideas to customize your mach for inspiration. I hope you will like the creativity of these customizations.