Include a business card with every product you ship.
Agree to include cards of other business associates in your mailings with the agreement that they do the same for you.
Selective sweets decoratively wrapped with a card attached makes a good promotional gift.
Scan your card to use as you would an advertising banner. Exchange links/banners and have the other site link the image of your card back to your website.
Use as a bookmark in business related library books. I’ve never actually tried this, but I suppose there’s always a possiblity that it could work.
Give two cards so that your contacts can in turn distribute them to other people.
Get a transparent plastic cover with a pin, insert your card and attach it to your lapel to wear at conventions or meetings.
To be subtle, ask for someone else’s card first, then return the favor by presenting them with your card.
Post them on bulletin boards.
Place an advertisement in newspaper or magazine using your card as the ad.