For travel agents looking to maintain client interest during a lull in their travel business may wish to send out personalized greeting cards wishing clients a good holiday and thanking them for their business, John Frenaye writes. "No sales pitch. No flier. No call to action. I bet when the New Year rolls around and they do begin to think of spring break or summer -- you will be on the top of the 'must call' list," Frenaye writes.