I like this stamp from Stampabilities but it seems to bulky for a smaller card. I used half of it on the outside of the card and the other half on the inside of the card. The star and the manger scene are from a Stamping Up set of six. So from one stamp I was able to make two.
I love this Cardinal Stamp purchased at Hobby Lobby. It's fairly easy to stamp and watercolor. The outside says "Once in a lifetime you meet someone who changes everything" and the inside is stamped "Wise Men Still Seek Him"...with the other half of the stamp above.