Sites like these are a good way to link back to your own site, basically free advertisement. They let you add your own site with a link etc.

• The Cardboard is a free online business card bulletin board. Search for contacts by location, industry or keywords. It’s easy, create an account, upload your scanned business card and post it to the site.
• Cardly is a site where you add your portfolio online, which you’ll be able to integrate your to various networks (Facebook, Twitter, YouTube, etc.). Basically, a little about you and how to contact you. Choose between many skins and features.
• Businesscard 2 is self-promotion tool that helps individuals to package themselves in a single, portable, 300 x 250 interactive web container. It’s a digital business card.
• Nuebbo has been designed to turn actual business cards into virtual cards. Nuebbo allows you to present your own business card to your Facebook profile and also view those from your contacts.