While browsing the web, I came across the great tutorial from Jessica Jones, over at How About Orange. Thank You for such a wonderful and detailed tutorial.
Just kidding. Sometimes gift cards are the very best present.
To make a holder for a standard 3.5 x 2" business card, start with an 8.5" square of paper. For a standard gift card, use a 9" square.
Place the paper pretty side down. Fold the sheet in half vertically and open it back up.
Fold the left and right edges inward to meet the center fold.
Open the paper again. Fold each corner inward so that the corner points meet the nearest crease.
Close the left and right flaps.
Turn the paper over and fold the top down so that the exposed diagonal edges meet precisely at the fold.
Fold the bottom up in the same way, tucking the bottom edge into the diagonal flaps. They should overlap slightly.
Insert a card to make sure it fits, then fold the case in half. All done!
To make a fabric version of this case, see this post.