Robin Good: The responsinator is a free web-based service which allows you to easily test any web site or web page URL designed to test responsive websites on 10 different device resolutions ranging from the iPhone and iPad and extending to Android and Kindle devices.
All of the previews are showcased on a single scrollable page.
Free to use.
Here is an example: http://www.responsinator.com/?url=www.ibm.com
Try it out now: http://www.responsinator.com/ ;
Via Robin Good