This is by no means a definitive list, but I've tested these programs and found them all to be worthwhile. Some more additions after feedback. Please keep the suggestions coming. (These are mainly Windows programs: At some point I'll do a Mac list, suggestions for that also welcome)
- Awasu A free Windows RSS client, allowing monitoring of a variety of news sites and weblogs around the world. Using plugin architecture, can also be customized to monitor databases, email accounts, and other resources
- FeedReader Freeware application for Windows.
- Newz Crawler Provides access to news content from several sources, including XML, RSS, Usenet, and the Web.
- NewsGator News aggregator that runs in Microsoft Outlook. Site features product overview, online tutorial and trial download.
- Novobot A heavily featured desktop newsreader, that can also scrape non-RSS'd sites
- RSS Bandit A free desktop news aggregator for Windows built on the .NET Framework.
- RocketInfo The Rocketinfo RSS Reader is a FREE personal news and information tool that allows you to search, subscribe, read and track content from thousands of RSS and Weblog sources.
- FeedDemon FeedDemon enables you to quickly explore the world of RSS from your desktop without having to visit hundreds of sites. Written by Nick Bradbury, creator of TopStyle and HomeSite, FeedDemon makes RSS as easy to access as your email.
- Abilon Abilon displays headlines from RSS (Rich Site Summary) Channels in an easy to read format. It is small (364 kb), fast, and free. Adding new channels is as simple as right-clicking and entering the address of the feed.
- RssReader RssReader collects news in the background at user configurable intervals and warn with a little popup in the system tray that there is a new message arrived. You can click the news headline to see a short description of the news and click or open the original news web page in an RssReader browser or default browser window.
- SauceReader Clean, intuitive Outlook 2003 style user interface. Integrated weblogging environment with full posting functionality. Share content with friends using the Windows Messenger integration. Automatic application updates. Feed discovery and one-click subscription to RSS and Atom feeds. Full-text search of archived items.
- RSSOwl (thanks, Sam Prince) It lets you gather, organize, update, and store information from any compliant source in a convenient, easy to use interface, save selected information in various formats for offline viewing and sharing, and much more. RSSOwl is also free of charge, fast, cross-platform, and unobtrusive. It's easy to install, easy to use, and easy to move.
- Bloglines (thanks Mark) Bloglines is the most comprehensive, integrated service for searching, subscribing, publishing and sharing news feeds, blogs, and rich Web content. It's free and easy-to-use.
- SharpReader SharpReader is an RSS/Atom Aggregator for Windows, created by Luke Hutteman.
- BlogMatrix Jäger (thanks, Dewayne Mikkelson) BlogMatrix Jäger is an extensible "one-panel" reader, taking up a very small amount of screen space, and includes a synchronization feature. (+ Mac)
Here are some others I haven't tried, but which have been suggested by readers: