I enjoy the benefits of the additional real estate of a second monitor at my desk. Now there's an easy on-the-road option.
It's called Duet and it allows you to use your iPad as a second screen. You install Duet on your PC or Mac (for free), on your iPad (for $9) and plug in your iPad with a USB cable it just works.
It works with either a Lightning equipped iPad or one of the older models with the 30 pin connector. I'm using it with an iPad 3 and a MacBook Pro – they say it also works with Windows PC's.
The performance isn't super but I understand it's better with a newer iPad using a Lightning connector – it's adequate for anything you're doing that doesn't require a lot of mouse movement. I'd love to see it working with an iPad Pro (but I just can't afford one.)