Making a card out of business cards is easy and will impress your friends!  Text and diagrams are also available here.

Start with six business cards.

Pick up two cards, and place them across each other at right angles, making a fat cross.  They don't have to be exactly centered, but the angle is important, so try to get them truly perpendicular.

Fold back the ends of the front card, all the way around to the back.

Turn the two cards over together, and bend back the ends of the other card, making a tight little bundle.

Pull the two cards apart.  You've prepared two of the six.  Repeat this folding procedure for the other two pairs of cards.  Now you have six folded cards.

Constructing the cube requires a bit of dexterity.  Each card will be a face of the cube.  Everywhere two cards meet, the tab of one card will be on the outside of the side of the card next to it.

Begin by setting up two cards as shown to the right.

The third card is added perpendicular to the first two.  Remember: the tabs are always on the outside of the cube.  If you have a tab pointing inward, something is wrong.

The fourth card is added vertically.  You need to be careful holding the four cards in position at this point.

The fifth card goes on the front of the cube, and neatly holds everything together.  At this point, the cube is nearly free-standing.  The two vertical cards on the side will have a tendency to flop inward, but that will be fixed by the sixth card.

The sixth card goes horizontally across the top of the cube.  Tuck the card under one of the tabs sticking up vertically, and lay it across the top.

To get the very last tab positioned properly, you'll have to reach in gently to pull the tab all the way out, and then drop the sixth card into place, and push the tab back over it.

Now you are done!  The cube is much stronger than you'd think, considering there is nothing really holding it together except the folds in the cards.

You can add more cards to the outside of the card to give it a finished look, or join multiple cubes together to build larger structures, but that will have to wait for another tabblo.  Enjoy!