Freebbble!

iMac 27″ size wallpaper.

Refresh Your Desktop Wallpaper is a free Wallpaper design resource made by Dribbble user BEASTY DESIGN. As far as I can tell, its license is Personal Use Only.

Helpful hint: Dribbble users are nice. If the license is unknown, it is usually because they forgot to mention it explicitly; not because they were being stingy. Ask nicely and they will probably allow you to use it.