Dapper: convert any web page into a web service
"Dapper allows you to easily build an API for any website. Initially, if the content source you’re interested in is not Dapped already, Dapper will take you through a visual and intuitive process that takes just minutes. When finished, you will have at your disposal an API with which you can interface to get the content you are interested in."
Basically a screen scraper. Obviously this only works with reasonably static web sites. As the trend has sites become more interactive and use other rich formats such as Flash etc, this tool system will become less and less effective. This app has caused a sensation -- been bookmarked like a billion times on Delicious today.
I've had a quick play -- here's the source for a Google Desktop Gadget that presents a
London Tube Service Update [XML].
Legal implications
Stripping out branding and repurposing content will definitely violate that little 'legal' tab at the bottom of most web pages.