I play Middle Eastern strings (oud, cumbus). The classic kind of plectrum for the oud was the core of an eagle pinion feather soaked in olive oil for six months. Others were made of tortoise shell or buffalo horn. You can buy various plastic imitations but I prefer to make my own by polishing short strips of the kind of heavy duty strapping they use for bundling paving slabs, timber and pipes. There are several different types, whenever I pass a building site skip I look to see what they've got. There's a picture here.

My cumbus page