How about carbon fiber? This is used by many manufactures.
Or better yet composites such a metal wood laminates or other combinations. I believe these would provide the best solution for resonances while allowing the designer to maintain an optimal mass.
I have also seen lexan used. Scheu has one that is truss shaped.
@Hiho
"But the wood arm can give you splinters!"
When carbon fiber breaks it splinters a whole lot more than wood. Fibers in the eyes and lungs is not very pleasant.