If you have found a site that has some interesting information and you would like to put it into a .rss feed but they don't have a .rss feed for you to use. You can create one. I stumbled accross this recently while looking for newsfeeds to include on my site.
Go to www.myrss.com and click on Create a Channel then enter the URL of the site you would like to see in a .rss. Their robot grabs the content from the site and does it's best to create an .rss file. It then gives you the different .rss file option to put in a php_portal block. I used it to create a newsfeed for some specific information.
One note, if the site you are trying to grab has a lot of menu stuff in it you may get a feed with that information. But they say it is suppose to learn and get better. I'm not too sure about that though.