Ideally the loli card would have:
A Photo (A good photo that we will be able to match with you.)
Real Name (first only)
Phone Number (If you want, I usually don't give out my phone number unless I know the person)
Or it could be double sided - the back side could have a full bleed bust shot of you in lolita and the front can have your information. (But your face should be very visible - the point is to associate your name with your face.)
Business cards can be printed online pretty easily for cheap.(like mini moo cards!) I think it'd be a great way to get to know lolitas everywhere; especially when we go to conventions and have once a year meet-ups. I'm gong to make one even if no one else does. ^^;;;
Edit: Or if you aren't loli and wan to make a jrock/takuya angel/aristocrat/steampunk/etc card, it'd still be great to have the information!