Use this on a flash drive if your co-workers don't lock their computers - just drag an image onto the executable and it will set the image as a centered wallpaper, even on multiple monitors.

Social wallpaper site--user submitted and user voted

Daily deviation 2006-12-27, wallpaper of a soft-bound book with a magical bolt striking it.

Open source project: renders the screensaver of your choice on your desktop.

For the CAP member in the family...

high resolution desktop wallpapers that stretch across two monitors

I especially recommend "Waveform" (second page I think)

nifty - run an OSX screensaver on the desktop while you work. Or get distracted, as the case may be.