Finding news can be a pain (quoting the Gnus manual). Some words on XML feeds:
To find usable XML feeds for content syndication (the news boxes on the right are filled by the XML feeds of the linked sites) you have two choices. The first is the obvious one: You look for interesting sites, and if you like one, you look for a possibility to get their headlines in RSS format. Nice guys represent the availability of a feed by linking it with an orange XML button like the one you can find on the left side of this page. Not so nice guys are hiding the link a bit deeper in the site documentation, and the absolutely not nice guys don't have an XML feed at all.
The second choice for finding news is the usage of feed directories. One of the biggest is Syndic8.com. The feeds in there are matched into categories from DMOZ and other sources. This is done automatically; as a result there are many uncategorized feeds. To find your news you should use the full text search in addition to the category system.
Another well known directory is NewsIsFree. All listed feeds are categorized on entry so there are no uncategorized items. NewsIsFree is assembling feeds for many sites without own feeds.
The site design of NewsIsFree is more end user friendly whereas a real admin has more powerful possibilities at Syndic8.com like seeing the activity of a site by stepping back in the poll history of the headline display.
Update: More information about feeding and getting fed (up) can be found at webreference.com and soon in my bookmarks. O'Reilly have an aggregator named Meerkat for their several feeds. To test your own feed you can use the RSS Validator at Userland.
UpdateUpdate: The aggregator at Userland doesn't respond at the moment. However there seems to be an all new, much better RSS Validator at archive.org. It grumbles about my RSS feeds - and it's right! I will have to escape some entities in there.