In iPhoto for iOS you can beam a photo from one iOS device to another, as long as they are both on the same wireless network. Watch the video below to see Beam in action.
The good thing about this feature is that if you are in the middle of editing a photo, and you beam it to another device, it opens just as it was on the initial device. This allows someone else to finish editing it, or perhaps for you to finish editing some of the finer details on your iPad.
As ZahidMaqbool points out below in the comments, you can also use Bluetooth for the Beam feature. This takes away the need to be connected to a Wi-Fi network, while still allowing you to transfer photos directly between devices. Just make sure Bluetooth is enabled on both devices, no need to worry about pairing, and Beam the photos using the same method laid out in the video above.
What's your favorite feature of iPhoto for iOS so far?
Update, March 19, 2 p.m. PT: Updated to reflect Bluetooth capabilities.