A superfun type of card is the so-called Box Card. Its design has been around for quite some time I think, and I don’t know who originally came up with it. This kind of card looks like a box but behaves like a card, in that it is made from cardstock and fits perfectly into an envelope!
By the way, it’s in no way comparable to a so-called explosion box, of which you can view some examples here.

Using the richly colored Fly Free paper collection by Kaisercraft, I created two: one as a birthday card, the other as a New Baby card. If you like die-cutting, fussy-cutting and overall embellishing, this is an absolute Must Try for you! 🙂 To help you along check out my very affordable Tutorial #26, containing easy-to-follow instructions with 69 very clear pictures, which you can acquire here.

Have fun watching the video and do let me know what kind of box cards you would like to see, or for which occasions you have created one yourself! 🙂