Here's a site that is fun, but not essential:Tag Galaxy
If you put in a search word (it could be the name of a city, a product, a flower, or your postman) into the 'Tag' box and click 'Go' and Tage Galaxy will select photos from Flickr (a site full of photos) and put together a world showing you the images it found.
Here's an example of an image the site will create if you put in the 'tag' Munich.
And here's what Earth Album put together for Munich... which is another fun, but not essential site.
And if you have a fun, but not essential site to add to the list, please post the details up here.