I draw and paint quite a bit on my iPad and what I've always wanted is a mahl-stick--something to rest my hand on while I'm drawing. This isn't a problem with your typical Wacom tablet which works with electromagnetic signaling between the pen and the pad and your hand resting on the surface doesn't affect anything. Because iPads and tablets have touchscreens (capacitive or resistive) it usually means you can't touch them with your fingers, hands, toes, or noses unless you plan to draw with them. You're forced to work without putting your hand down. The answer is a brace that can move anywhere your hand moves, that's strong enough to take the weight of your resting hand (and arm), and that can be easily positioned across the screen at any angle.
I've built my prototype hand rest and here it is. It cost me somewhere under $4 to make and that's with enough material to make five or six of them. What do you think?