I don't think they need to be vertical and hanging just because they are pendants. I agree that the backgrounds given here are too busy, but I also don't necessarily like the idea of just a plain background. Be creative, but always remember that the pendant is the purpose of the image, so the background should complement, not compete.
I look at this as if I were trying to decide whether or not to buy the pendant. One of my first concerns would be, "How big is it?" I think you need a background that will highlight the pendant and not distract from it, but it would also be nice to have something that offered a sense of scale. The one that includes the bill helps do that, but unfortunately, the composition of it makes me think that the bill is the focus of the image, not the pendant.
Also, I feel the ones that are backlit and really show the glowing quality of the jade are the most effective. You want to be very very careful with lighting - it doesn't always have to be backlit, but the picture should show how the stone reflects light, which is part of why someone would want to buy it.