In response to a comment on the following post, I thought I'd share a bit about what an artist trading card is for those that don't know.
Basically, it's the same size as a sports trading card. 2 1/2" x 3 1/2". They are traded, not sold. They should be your original art, photographs, collage, limited edition prints, or mixed media. And though the ideal is to trade them in person so that one can get to know other artists, there are plenty of online places to trade.
Here's an excellent resource for those who are interested in finding out more about them.