IMHO, RSSPopper is one of the best outlook feed aggregators on the market.  (and it’s free!)

[From Author’s Blog Posting]

Enhancements:
* Support for newsgator.com synchronization
* Support Atom 1.0 (Preliminary)
* Added an option to redirect all links thru RSSPopper.com to prevent Outlook 2003 SP2 phishing warning.
* Improved feeds registration UI
* Improved installation process

Bugs Fixed:
* Better handling http caching (handle invalid protocol values)
* Fixed problem displaying central European languages special characters (Umlaute ect.)