I bit the bullet and got my own business cards about a year ago for the same reason. I have worked for employers who have given me business cards and those that haven't, and I was at that time working for a company in the no-card camp. But I would have gotten my own cards even if I had cards from my company because what I wanted was to be able to give someone a card that reminded them of me, not who I was working for at that moment. I've seen other developers who also do this, and there's a variety of things that I've seen people put on their cards. Mine has my:
- personal web site
- personal email
- phone number
- LinkedIn profile address
I've seen others put links to their blogs, twitter handles, or list their preferred title (e.g. developer, architect, entrepreneur, etc.)
You can be simple (I was), or be creative. There are lots of sites out there with inspirational design examples. If you can, it's worth while putting a little effort into making a card that shows a little creativity and is a bit more memorable than the average corporate card.
There are lots of places you can get high quality cards at a reasonable price, and in reasonable amounts. I highly recommend MOO, and especially their mini-card, which I think is the perfect size for a card that's a reminder of a person.
You probably won't need very many cards. I got 100 cards and haven't gone through more than half in the course of a year. Mostly that's because I don't just hand them out to anyone, I give them to someone who I've spoken to for a bit and who I want to keep in touch with because they were an interesting person or work for a company I think I might be interested in.
And of course, I use it for dropping into those "free drink/meal" raffle bowls you see at some bars and restaurants. I'm a sucker for a free lunch, even if it means getting stuck on yet another mailing list.
One more point (I'm adding this during an edit) to emphasize what some of the other folks have pointed out. You need some way of handing off a physical reminder to people you meet face to face. But more importantly, you need to be meeting people face to face. Every developer (or other IT professional) needs to get offline and interact with others in the industry, and business cards are invaluable in those situations.