Page2RSS is a very nice service that creates feeds from any web page, by including the new content and linking to a page that highlights the differences.
A simple example of web page that could be monitored using Page2RSS is google.com: a homepage that rarely changes only to celebrate important events or to announce new Google features. You could subscribe to the automatically-generated feed by visiting: http://page2rss.com/page?url=www.google.com/. This also works for international sites like Google Japan, Google Italy etc. Unfortunately, you'll also receive an update when Google puts the classic logo back.
Of course, the service is useful for any web page that doesn't offer feeds, but it's better suited for web pages that don't change very frequently since Page2RSS checks to see if there's new content every 4 hours. You could use it to generate feeds for changelogs, privacy policies, news sites, Google Labs or to find new features in Google's services, like Hindi support added to Google Translate on April 29. Can you find other interesting web pages that could be monitored using Page2RSS?