spacedesk is a free program that makes it really easy to use your tablet or smartphone as a second display for your Windows PC. It offers two modes to do this: Extend and Mirror.

Android tablet-side setup Step 1: On your Android tablet, install TeamViewer from the Android Market and launch it. In the first box, enter the ID of the "partner" computer.

But you can use your tablet to improve your productivity, too. Since a tablet is essentially a portable touchscreen, why not repurpose it during work hours as a secondary display?

First appearing in Android 3.1, USB Host mode is a neat feature that allows you to plug in USB devices (including game controllers) into your tablet via a USB cable.

The iPad is a good bet, of course. For Android tablets, the Google Nexus 10 is a great deal. And the Samsung Galaxy Note 10.1 is also a solid bet, because it also comes with a stylus.