One of my guilds makes them out of quilt blocks that are about 1/2 the size of a potholder. Make the center in a white or light color so that people can write their names in, and attach a slim strap so members can hang them around their necks.
One person in our guild makes them and sells them to new members, but new members could just as easily make their own from scraps. It would make a fun, quick activity for a meeting, too.
For visitors, use the stick on name labels you can buy at a place like Office Depot or Staples.