Multiple displays for my desktop.
When dealing with desktop publishing as a technical writer, I frequently need multiple application windows, a terminal window or two, a client window for the app, my editing program and it's attendant windows, and several misc application to support my work (eyedropper, wireshark, screen cap, gimp, a text editor).
Three monitors would be ideal, but I just don't have the space on my desk. I'm considering a triple wall-mount, another monitor, and rearranging my space so the desk is pushed up to the wall.