Duet Display app allows you to use your iPad or iPhone as an extra display for your Windows PC. This app is developed by a team of ex-Apple engineers, duet is the first high performance solution that has zero lag.
To setup, download and open duet on your PC (for free) and on iOS. Connect your iDevice to your PC using a lightning or 30 pin cable.
Duet Display now supports Windows 7 & 8. To celebrate the launch, Duet Display for iOS is now available for $9.99(40% off) from Apple App Store. Download it here.