iOS: CardFlick is a free app for creating business cards directly on your iPhone or iPod touch. It comes with several themes and sending is as easy as sending an email or just flicking your card to another user's phone.
To get started, you just add a photo and enter a little information about yourself so the card can be filled out. Then you choose from many themes to get the look that you want. Once you're done, you'll be able to send your new business card to whomever you want.
Sending is very easy if you encounter someone else using the CardFlick app. You both open the app and go into flick mode, then push your card across the screen to send it. If the person near by isn't using CardFlick, however, you can just email it to them. It's not as fun, but it's not much harder to do.
The primary downside is that you need to sign up for an account in order to use CardFlick, but that does come with the benefit of having a landing page for your card (here's mine). If you need a free, attractive business card that you don't have to bother printing, however, it's only a small annoyance.
CardFlick (Free) [iTunes App Store]