Die cut business cards.
Your website and proof turnaround would be light years ahead of anyone else offering die cut cards. Logo on the front, details back, allow choice of one ink color for back (not just black)
That'd be epic!
Peter Crysdale commented
I was just researching the same idea, and it can be done with stickerrobot.com. I don't have any affiliation with that site, but Sticker Mule currently doesn't print on the back of their stickers!