You want something to be viral?
*Try to make the business cards on thick stock with the one front being a giftcard to the store and the back being your advertisement. Feel free to hand them out or drop them all around the store.
*Banners near exit ramps
*You could also promote my site for me that I sent you last night
*Dress up and act as a rep and give out flyers to exiting/entering customers.
And put a QR code pointing to a CPA offer so people can scan it with their smartphones. Double your money!