A little company called Stardock has an utility called Multiplicity which I use all the time. Basically, it’s a program that allows you to control multiple computers using just one mouse and keyboard, via your network connection. If you have a home or office network, and you use multiple computers, this is the product for you.
To use, all you have to do is move the cursor off the right side of the screen (or left side, depending on your configuration), and the cursor moves on the second computer. Once there, your keyboard is “connected” to the second computer automatically.
I find this to be more useful than having 2 monitors on one computer because you have a separate computer doing it’s work without having to share resources.
You can also share the clip board. For example, if you are looking at a website and want to put that on the second screen, just highlight the URL, type ctrl-C to copy, then move your cursor off the screen to the second computer, open the browser, and ctrl-V to paste the URL, and now you have the same website on the second computer.
Normally, I put my laptop next to my desktop and use it as a second screen. I can do searches, watch video or do other things on the laptop, while I do my real work on the desktop screen. Nice.