Google has released a Free RSS Combiner Plugin for WordPress. This Free WordPress RSS Combiner is a Free WordPress Plugin that lets you merge several RSS-Feeds into one.
It caches the input feeds, sorts items by publishing-date and then outputs a feed in either RSS 2.0 or Atom 1.0 format.
RSS Feeds, when added to a web page helps new content to show up on the pages. As such, since the feeds refresh with time, blog pages with RSS Feeds always show up as “new content” in the eyes of search engines.