If you're using Apple's Bluetooth keyboard or a laptop, you might find yourself occasionally in need of a number pad. NumPad Remote is a download for iOS and Mac OS X that turns your iOS device into a portable number pad.
To set it up, you need to download both the free desktop client and the $2.99 iOS app. With both apps running and Wi-Fi enabled, you enter in a four-digit authentication code and the rest happens automatically. There aren't a lot of configuration options, but you can switch the key layout from calculator style to dial pad. If you don't need a number pad all the time, it's a helpful tool.