I did a search for best responsive websites, the one I found was accroachcode.com. It was drastically different given certain width while still maintaining a charming look.
This is a screenshot of the website at desktop view. At the top it has a menu, banner, and a link to a project list. Below that is the main home page graphic. Below that is two text columns detailing the site's information.
Not much is different down on tablet size except the complete exclusion of the header area. The menu, banner, etc. have all vanished. All that remains of the header is the logo.
The mobile phone size is drastically different. The header has now completely disappeared, and the main home image has moved below the main text. The area below that is now down to only one column.