The weathered texture of these steel pendants is strangely touchable. Some are available with a gold finish as well as bronze, others have free-moving parts that highlight their topology. All are math, art or both.
I want to recommend the Shapeways links for these. Their plastics are faithful, bright, and a steal at under $10; their metals are beautifully produced and a great selection: more steel finishes than I can stock, as well as polished brass, bronze, silver, and I'll turn on gold on request.