Business cards are handy for the non-businessperson, too. From Shawna:
Our family uses VistaPrint to order free business cards with all of our contact info. The cards are free when you pay for shipping, so they work out as a pretty good deal.
We use them to facilitate playdate set-up, as a quick reference for babysitters (in addition to our list of emergency info), as luggage tags and I put one in the back pocket of each kid when we go to crowded venues.