Get two computers for the space of one. If you're looking to add an additional desktop computer to your home, but don't have the room (or the money), Desktop Multiplier allows you to share one computer between two monitors. If you already have a dual screen setup, you won't need much more than an additional keyboard and mouse, and you'll have to switch over to Linux. The software takes advantage of Linux's ability to handle simultaneous users. You are able to share one computer with up to ten machines, and Useful has a handy page that lets you see exactly what you need to get up and running. They also tout this setup as a "greener" choice, which is believable since you are only using power for one machine. The software is available as a free trial, but you'll have to contact them for purchase information.
Thanks blue gazelle for the photo!