The development of this component started out of the need to consolidate different RSS Sources into one feed that is ordered by publishing date.
The source feeds are not limited to feeds on your site - you can wire up and mix feeds from any site you like.
You could then run this feed through feedburner and let users subscribe per email for example.
Feeds are processed with the simplepie library that is included in Joomla.
Download the component: RSSConsolidation for Joomla