Order new business cards. With a mailing address on them.
I recently went through a pile of 60+ business cards gathered by a colleague at a show she visited last month. Most of them contained only the barest of contact information... company name, website, and sometimes an e-mail or phone number.
I accept that in today's technological world, a website and/or email seems like it should be a sufficient amount of information to provide if someone wants to get in touch with you. But what if that person who picks up your business card is someone who actually needs to MAIL you something (an application, or a contract, or a proposal, or anything that is printed on paper)?
They now need to either go to your website to find your email or (my personal pet peeve) complete a web-based form to send you a message. Eliminate the unneccesary steps, because in many cases, people just won't bother. And a business card without complete contact information also seems a little unprofessional.
But, you say, hundreds of customers pick up my business card at shows, and I don't want complete strangers to have my home address. I accept that too. Today, then, go to the post office and get yourself a P.O. Box.
Then you can have your new business cards sent to it.