Mountie Device Clamp
Ten One Design's Mountie is a little rubberized gizmo that strongly latches onto the side of a MacBook or post-2012 iMac, with a slot on the other side with swappable clamps for an iPad (Air or mini) or an iPhone (4 or later). The idea being, keep your work on the Mac and the fun stuff on the side — FaceTime, Netflix, etc — or something like Duet Display to extend the Mac's display.
The Mountie, expected to ship in early February 2015, is $25. Comes in green or blue.