First, acrossair which brought us the Tube Finder, is now showing off a very slick "general purpose" AR browser for the iPhone 3GS:
Next, GraffitiGeo, a fresh new startup that wants to create a Digg like service for real places is working on an AR version of their application, also for the iPhone:
(more details about GraffitiGeo here).
So, now we are at five AR browsers. Anyone wants to bet how many browsers there will be by this time next year? (my guess - only three serious contenders, and one of them will be owned by Google).