This is about as close as we're going to get to real ponies unless someone invents a portal to Equestria. Thanks for this heads-up goes to Tailszefox.
For those unfamiliar with the concept of augmented reality, it's pretty much what it sounds like. Computer-generated elements are superimposed upon the real world in real time and tracked intelligently using a variety of sensors (like cameras, gyroscopes, or solid state compasses) in order to give the user more information about their environment. You can use this technology with a smartphone, for example, to detect text in a foreign language and replace it with your own in real time. The technology isn't widely used yet, but it's gaining ground as our processing power and detection algorithms improve.
A pony has taken this concept and added ponies. You simply print out the markers and use your existing webcam and computer to track and replace the three-dimensional position of the marker with your favorite pony.
You can find the application here. It runs in Flash and is a hefty download, so be patient. Print out your markers in the meantime.