If you want to aggregate RSS Feeds from different sites and use it for any purpose, Yahoo Pipes is something that you can use.
You can use your Yahoo account for this purpose. Login to Yahoo pipes and create a new pipe and in that you can use different features like filter, replace, truncate, string replace and many more options.
I created a pipe which you can see below, which fetches 3 feed items from more than 10 feeds, filters the duplicates, and gives the results.
These is a function called union, when you can mix up different results and get the final results. I use this feature to aggregate news from different sites with similar categories from my latest blog posts site.
Related posts:
Kishore Asokan is the author of this blog and has been blogging since 1999.
He is a software professional from Carnegie Technology of Education, Pittsburgh, USA. He works on
.NET, PHP, AJAX, etc. He has been making money online for the past 10 years and is still learning
to monetize his skills. He has recently launched his 
tx Kishore .. I’ve had problems with my Twitterfeeds and had peculiar results when I tried mixing that with Hellotxt .. you got me onto Pipes and whilst frankly at fist I didn’t know what on earth you were going on about .. damn, this is powerful and your post here, and especially mixed with the image, is an inspiration.Thank you.