You can use the combination of two apps, Camera A and Camera B, to allow your iPhone’s camera to be shared on your iPad.
I thought this was cool because this gives the iPad an input device. You can see the iPhone viewfinder on the iPad and you can snap pictures.
This Bluetooth-enabled combo will be much more interesting once the iPad adds multitasking, which is in the works.
If you decide to try it out, come back and drop a comment.