I had a hard time trying to match up my card stock with the iTunes gift cards for my daughter and son-in-law. I decided to use Melon Mambo for hers and Wild Wasabi for his. These gift cards are larger than the normal ones so here are the measurements I used:
6 1/2" x 9" card stock
Score on the 9 1/4" side at 1 1/2" and 5 3/8"
Decorate as desired.
I attached the image panel to the ribbon on the front. Once untied, the gift card holder can be easily opened.