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
IntraVNews
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