How is it that the aggregator BlogLines hasn't been mentioned? I love using
BerryBlogLines on my Pearl and aggregating my feeds with
BlogLines. They use ruby-on-rails to make it fast on the blackberry - and the functionality really rocks... and it's free as in beer.
Secondarily, I like to use the built-in RSS feature on the blackberry browser for large volume feeds like Digg.com - go to digg.com and hit the menu button and select subscribe to rss feed in the browser... works like a charm.
Thirdly, Opera Mini Beta 3 has a very nice RSS feed functionality that is worth checking out.
http://beta.mini.opera.com
No matter what you think of these... each and every one of them is better than ANY windows mobile 5 rss reader I ever used. Love RSS and love the way the blackberry makes it rock!
-Stac