InterfaceLIFT
Much respect to the team at InterfaceLIFT. This is without a doubt the best place to find desktop wallpaper.
I have my Mac change the background every hour. It does a nice fade effect into the next wallpaper. When it changes I genuinely feel good inside, and look forward to the next change.
http://www.pixelgirlpresents.com/desktops.php
sometimes these have some nice ones, kinda arty farty or comical, dont think they have many at 1920×1200 though.