This post summary and provides links to most useful feed services .
Creation of search feeds
Web to RSS: Google Alert, MSN Search, IceRocket, Yahoo! (beta)
Web, news to email: Google (News) Alerts
Google News to RSS: Google News RSS Generator
News/press releases to RSS: PubSub, Daypop, Yahoo! News, MSN Search
Company news to RSS: Yahoo! Finance
Newsgroups to RSS: PubSub
Blogs to RSS: PubSub, Blogdigger, Feedster (also searches feeds generally), Technorati,BlogPulse, IceRocket
Linking activity to RSS: Technorati (blogs), Feedster (webfeeds generally)
SEC filings to RSS: PubSub
Articles to RSS: FindArticles
Aggregating/filtering multiple feeds into single output feeds
Without filtering: Blogdigger, RSS Mix
With filtering: Feedster
Creating secondary feeds with different output characteristics
Creating feeds for web pages which do not have them (scraping)
Email to RSS tools
Online archives and archive feeds
Web pages to archive to RSS: Furl
Article abstracts/citations: CiteULike
Dedicated feed creation software
RSS to email tools