OverPlot is a mashup of Overheard in New York and GoogleMaps. I think it's a really good example of a simple and very effective interface for displaying geographic information. The geographic location isn't imperative for browsing through Overheard, but it is a good method for navigation.
The clustering of items at a location, the next/previous within a bubble, and the location in the corners of the bubble are all nice little effects. At the "widest" zoom level, you get the neighborhood links. Then you click on those to zoom to a view where you can see numbered items of overheard statements. As you scroll-around, new map markers are shown. It's very slick and very fast.