I designed a simple business-card holder that nicely matches my business cards. Simply slide the cards out. It fits cards 55x85 mm.
Make sure you orient the print correctly: easiest is with the slit at the bottom, so you may have to flip the STL upside-down. Sorry for that.
I included the solidworks file so the text on the back or the dimensions can easily be changed.
The print in the pictures is printed on an ultimaker, 0.1mm layer height.
The bcard3.stl has no text on the back, the bcard_theboss.STL has "The Boss" on the back. For obvious reasons, I did not include the one that has my company name...
If you have a special request/ideas for text, I could upload a few variations, but only if the text is fairly generic so more people could use it. If you want your company name, you'll have to pay big time :-)