I found this one on Engadget and have to say it is one of the cooler Augmented Reality vides I have seen.
It is a "card trick" performed extremely well and with special real-time effects added. You get to see the actual scene and the augmented one in the same frame which makes the imagery more impressive.
What really takes the cake though is the fact that all of this was done with open source programming tools.
Read more here
Tempest uses AR to demonstrate what's going on in his fertile imagination as he performs a card trick -- cards levitate, Jokers dance, and the birthday cake? Well, you'll just have to see for yourself. The most impressive part is that the whole thing goes down in real time, and utilizes C++ with OpenFrameworks, OpenCV, ARToolkitPlus, MacCam, "and other Open Source goodies." Nothing's done in post-production.