I'm also becoming increasingly impressed with Newsgator. Their recent acquisition of popular RSS Aggregator FeedDemon was a further step in their plan to be a major RSS services company, particularly on the Microsoft platform.
There is the small matter of integration here - something I have a little experience with, having lived through the PPS/Digitalk mess. NewsGator is built on the .NET platform, and integrates with Outlook. FeedDemon is standalone, and is built in Delphi. Ok, you explain to me the technology integration path there :)