A short overview of augmented reality apps, mostly on iPhone or Android platforms: http://tr.im/A62C
Also see http://tr.im/A62K for videos of Wikitude (an AR travel guide that pulls place-based info from Wikipedia), Nearest Tube, Layar3D which superimposes data fro Twitter, Flickr and Wikipedia on the real world, ARider — an HMD displayed map for bicylclists — and an AR Marble game with remarkable graphics and interaction by Oda and Feiner.