News aggregators

Directory on Wikipedia

Free News Aggregators
Feedreader - Minimalist. Can't discover feeds. No built-in tabbed browser. Small footprint. Works fine.
Sharpreader - requires .NET framework, feed auto-discovery
RSSBandit - requires .NET framework, opensource, feed auto-discovery, tabbed browser
Sage - FireFox extension
GreatNews

Commercial
FeedDemon - One of the best. $30 (Bought out by NewsGator)
NewzCrawler

Integrated into Outlook
Newsgator - A great choice. $30. Integrates into Outlook.
You Subscribe
IntraNews
RSS Popper Free!

Web Based (Free)
Newsgator Online
Bloglines
Google Reader

Browser Integrated
Firefox extensions
Pluck - Integrated into IE
Maxthon - Custom tabbed browser based on IE. Has RSS sidebar
OnFolio- Integrated into IE & FireFox

For PocketPC
NewsBreak
PocketRSS

For SmartPhone
iPodderSP