The ornamental design for a business card holder, as shown and described.
FIG. 1 is a front perspective view of a business card holder showing my new design, the writing instrument depicted by means of broken lines being shown for illustrative purposes only and forming no part of the claimed design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof, the right side elevational view being a mirror image of the left side view;
FIG. 5 is a top plan view of the business card holder; and,