I've just come across a site called rssense.com
The concept is pretty cool and new.
From the site :
With RSSense technology you do not need to select the feeds yourself, we automatically insert the most appropiate feeds based on your site content. Furthermore, you can select which type of technology will be used to include the RSSense feeds in your site, and setup everything down to the detail.
* Free, self updating RSS content for your web sites.
* Installs quickly and easily.
* Can automatically select feeds for your site based on keyword matching, or your site contents.
* No login required.