iSelfie is a very clever free app that lets you take pictures from one iOS device, remotely controlling it from another. It solves the age-old "there's my arm in the picture holding out the camera" problem so common with selfies.
Here's how it works: both devices need to be running the app, and then they are paired over either Bluetooth or WiFi. One device is the host (where the camera is), while the other is the remote controller. The pairing requires acceptance from the other device, so no one can hack into your camera.
When the devices are paired, the remote camera device -- in my case an iPad -- could see the iPhone camera. I could even activate the flash if I wanted to. You tap the camera icon and the picture appears in the photo library on the remote controller device. If you have Apple Photo Stream activated, the picture is saved to both devices.
You have the option to add watermarks or date and time text to each photo.