So simple yet so interesting: Flickr Camera Finder.
Flickr Camera Finder indexes the camera models used in the images uploaded into the Flickr. It is effective and truly objective way to measure the popularity of the different camera models. Well, of course it is only the popularity among the Flickr members and considering that:
The graphs are only accurate to the extent that we can automatically detect the camera used to take the photo (about 2/3rds of the time). That is not usually possible with cameraphone photos and cameraphones are therefore under-represented.
If you are looking for a new camera, it is easy to find photos taken by different brands and models to compare them with each other.