Today's kids probably don't know what a "viewmaster" is, but they love to receive these interactive cards.
There is a tutorial in the resources section of this site (haven't seen it yet), but I first saw this technique demonstrated in the video tutorial "Spooky View Master" at dostamping.typepad.com.
It is a relatively easy card design and can be used for all occasions. All you need are (at least) 6 theme stamps that are small enough to fit in the window on the card.
To cover the brad and wheel on the inside of the card, I cut another piece of dp. You just have to be careful when you glue it in place. You can't get any glue near the wheel or it won't turn.