At ContentGems.com we aspire to offer some of the features you're looking for. We fetch a ton of feeds each day, index them, and let you filter the items based on a powerful query api (Lucene). So in addition to reading your own feeds, you can also extract interesting content from other feeds and discover new feeds. It also deduplicates articles (on a sliding scale of similarity). We are in the process of building out the feed reader component (which is trivial compared to what we're already doing with search). An interesting twist on feed readers is that CG treats your Twitter home timeline like an RSS feed, indexing all shared articles and including them in the Firehose of feeds. Disclaimer: I'm one of the co-founders.