Sometimes the best ideas are also the simplest ones. Tickr is a simple idea but also a great one. In essence Tickr lets you search Flickr by keyword and location.
Why is that so great? Well, it means you can make some great visual comparisons of different cultures around the world. For example, the images in this post show some of the differences in fashion in California and Japan. I've just spent at least one happy hour comparing 'houses', 'pubs' and 'businessmen' in different countries.
The examples on the Tickr homepage include 'architecture' in 'Rome' and also 'glaciers' in 'Alaska'. The latter example is a good demonstration of another feature of Tickr - the time-line. As well as showing the location of photos on a Google Map, Tickr also presents the photos in a time-line based on when the photographs were taken. This means that in the given example it is possible to compare photographs of glaciers taken in 2001 to photographs taken this year.
Other Flickr Maps