The spine and end papers (inside the book) match.
For inspiration, I looked to one of my favorite books, Expressive Handmade Books, by Alisa Golden. The cover is called a split-board binding (see pages 128 and 129). I used the accordian structure she describes. I added flags to the accordian structure so that I could attach the pretty cards to the book without changing the cards in any way. See Alisa's Single-Flag Book topic (pages 57 through 59) for tips on how to incorporate the flags.
I wanted to be able to open the cards so I could read the sentiments inside and the cards were not the same size. I attached the cards, back-to-back, two cards to a flag. I matched the card size as best as I could and adhered the backs of the cards together. This gave the cards strength for flipping. I will treasure this little book for its contents and for its cute look.
Think about the possibilities for some treasured event like a birthday or wedding. You could collect the cards in one place for sharing.