As somebody who’s been a big fan of working with multiple monitors for sometime now, I had my Mac hooked up to one of my big monitors. Given that I also have an iPad, I’ve just recently added it as my third monitor, by using the Air Display app for iPad/iPhone ($10). It works really well! And considering I already owned an iPad, this is the cheapest extra monitor I’ve added to my setup.
The iPad sits on the far left side, and I normally put a Terminal window there, where I’m running my commands, tests, deployment, etc. The screen on the Mac is where I normally have the browser showing the website I’m building, and the monitor to the right of my Mac normally has my IDE. That monitor on the far right is hooked up to my PC, which I use for my music recording, video editing, research, running the Virtual Brown Bag, etc.
I have tried to use Air Display to make my iPhone as yet another monitor (to maybe put small notes or instant message there), but that didn’t work too well for me. But I’m really digging having my iPad there. It’ll also come in handy when I’m on the road.