MaxiVista. Neato software which lets you turn a spare monitor or laptop into a second monitor for your main machine. Uses network/server architecture or something equally clever. $34.95.
MaxiVista enables you to use a second computer as an extended display of any other computer without the need of any special hardware. The software overcomes the limitation that computers do not have VGA inputs, and thus normally cannot be used as a monitor. MaxiVista installs a virtual video card onto your primary PC which fools Windows into thinking that an additional monitor is installed. Windows then activates the built-in multi-monitor capabilities and extends the desktop to an additional screen.