The Manfrotto Magic Arm is the choice in TV-land. Get the wheel-lock one rather than the cam-locked one, as it's easier to lock - you have to move the cam over it's high point, and this often makes the arm move suddenly, knocking it out of the position you've just set up. The wheel-lock is much smoother. They're good for a couple of kilos at least, and we put all kinds of lights or camera mounts on them.
They'll probably need a fitting to hold the GoPro, as it doesn't come with a tripod screw. We've used the little perspex waterproof housings before now, and put a K-clamp onto the arm, and then we just hold the whole thing in the jaws of the clamp.
For something lighter,
Noga also make similar arms which we use for Lilliput monitors. They often come pre-fitted with tripod (1/4"x20) or mic stand (3/8x16) screws, and will easily take a GoPro.