One thing that I thought was a nice idea and allows a year's worth of advertising is to have a calendar printed on one side of your business card (with your logo prominently displayed). This way a person can have your calendar card in their purse/wallet for a year, and when Jan. rolls around (and most people in this industry have a lull in business) you may get a few return customers that have gotten used to having the calendar handy and so they "get off their butt" and make another appointment hoping for another card. It doesn't cost much more for the calendar to be printed on the card and it may keep the card (and your business) more accessible/on people's minds. (Works better on people that aren't really into tech gadgets, as the techies have organizers/smart phones etc.)
Of course, this isn't going to make someone pay for a full detail just for a card, but if you have customers that want to get a wash/wax done, but always seem to put off the call, this may get them calling.