Basically the business cards I have are a square shape - you can get these made up from most printers, although they usually come under flyers rather than business cards. Just make sure to get a high gsm so they are nice and thick. I got these ones from Print Loft but I have also used Face Media Group. So because of their shape its always been hard to find a suitable holder for them that you can just chuck in your bag so you've always got them on you.
So I thought, the easiest way round it is to make my own! Its not a complex design or hard to make, but I thought I'd share it with you anyway!