This is a sort of "cross promotion" idea I'm testing. Basically another B2B service can save on the cost of printing, while I get some more exposure (B2B services will have a similar target market).
Details: "Save $25 on any set of business cards (or suggest another print item). Just display a simple advertisement for us on the back, and take $25 off the usual price. Use these cards as your regular contact business card, or create a mini promotional tool for a special offer or event. Printed on premium 420gsm card for a more professional result."