Once when working on two separate sites that would run off two separate domains, I was looking for a clean solution to have the two sites offer the same news. I knew the solution would be in using the RSS feed of one site to post to the other. There are a few aggregation plugins out there and after experimenting with them I found FeedWordPress to be the most flexible and easiest to manage. With a multitude of options, there are a number of uses for a tool like this. The best part is that when posts are created from a feed, the plugin attributes serveral aspects of the source in custom fields with that post. This allows you to develop your theme to attribute sources and provide links to the original content.
Plugin Homepage
http://projects.radgeek.com/feedwordpress
