Use your iPad as a second screen for your Mac...

I saw this article over the holidays from GigaOM about a new app that will let you use your iPad as a second screen when working on you Mac. There had been some before, but they were either very laggy or they required a jailbreak of the iPad. According to the reviews, this one has no lag and works perfectly as advertised.

So if you have been looking for a cheap way ($9.99 for a limited time) to get a second display for your Mac, this may be your ticket.

Duet Display is developed by Rahul Dewan, who was an engineer at Apple before starting Duet Display. It’s actually two apps — one for your iOS device and a companion app for your Mac that lets it recognize an iPad or iPhone as a second screen. To get Duet Display working, simply open the Duet Display app on your iPad and plug it into a modern Mac with a Lightning cable (or a 30-pin cable if you’ve got an older iPad that’s still supported.) Because you’re plugged in, there’s no need to worry about killing your iPad’s battery.
— full story at GigaOM - https://gigaom.com/2014/12/16/got-an-ipad-and-this-app-youve-got-a-second-mac-screen/