Pretty well the best ranking rss aggregator for me is Feedagg.com
I often get to page one for long tails just with a post to this site, so give it a try.
Here is a video on my blog showing the power of using these rss aggregator sites.
The Power Of RSS For Backlinks And Page One Rankings
If you want, you can grab my free rss wordpress plugin that gives you 5 backlinks everytime you post in wordpress.
A heap of reading on the blog, so enjoy!
Cheers
Tim