My last post on Augmented Reality showcased using mobile devices as the viewport. Other AR experience are leveraging increasingly-available webcams, particularly on laptop computers. Consider LevelHead, a game that projects the game environment onto cubes that serve as the game control mechanism:
From a developer standpoint, the biggest barriers to adopting these techniques are the complexities of computer vision and manipulating 3D space. As a developer, I'm particularly interested in ARtisan, which tries to simplify the use of Flash AR tools FLARToolKit and Papervision3D. Flash is uniquely positioned for the AR space because of the ease with which applications can be distributed and its access to the host computer's camera and microphone. If you have a webcam, I would definitely recommend checking out some of their examples.
Finally, this post has some other interesting examples of AR experiences.