Recs.
Updated
WeavRSS is a web-based RSS Feed Reader Service. The service provides a free account option as well as several pricing tiers based on user needs. The service also provides access to all paid features as part of a no credit card required 14 day free trial so you can give it a try without having to commit. The app's design is focused on delivering users the ability to create saved searches that match on current feed articles as well as historical feed articles. Searches can be written in either basic text format with boolean or using advanced regex syntax. While only the information provided in the RSS feed is displayed within the app, searches are run against the full-text of the article for improved discovery. The interface is designed for the efficient navigation of feed and search result history with an interactive article timeline chart. There isn't a mobile app yet, but the top level plan does allow RSS feeds to be exported out of search results. The interface is however optimized for use on tablets through the browser so using it on the go isn't out of the question.
SpecsUpdate
Pros
Pro WeavRSS's search functionality is second to none.
The option to write searches using regular expressions and run them against the article's full-text is extremely powerful.