AR cards. We've got the initial 6 that come with the 3DS. More may very well becoming with Kid Icarus as over 20 we're shown at E3. I bet Pokemon 3DS will have them, 3rd parties will have them at some point etc
So there may be a sizeable amount in the next few years. Add in their somewhat disposable nature (easy to lose/tear) and how people love to collect cards anyway, can you see them becoming collectable in 5-10 years? Although that doesn't neccesarily mean valuable.