I did a demo at work this week with a 70s theme. I'm not sure that anyone else liked this, but it was my favourite - an adaptation of the "Neverending Card" as a Rubiks cube card (and yes I know I've forgotten the orange!).
There are lots of different instructions available for the neverending card - some can be horribly confusing.
http://www.victorineoriginals.com/images/samples/instructions/neverendingcard.html has great easy to follow steps. Obviously there are more conventional ways to decorate these cards.