iDisplay Mini ($1)
Have you ever wanted a second display for your Mac or PC? You can keep tabs on more with extra screen real estate, but you might not want to actually splash out on a second monitor. With iDisplay Mini you don’t have to. You can transform your iPhone into a second display for your Twitter feed or IM chat. Install free software on your computer and buy the app and, as long as both devices are on the same Wi-Fi network, you can use your phone as an extra display.