Hundreds of examples and lots of patterns can be found on the web, using google or yahoo. They run from very artsy and complex to cute and quick. However, I would suggest you talk to the person in charge of the exchange to see if there are any rules about size, theme or style. I've seen many that are so pretty I'd consider a mini art project that would never get a splash of coffee! I was first inspired by some I saw on this quilting board!