Rui CarmoSharpReader is yet another RSS/RDF aggregator for Windows platforms (and, like Syndirella, written on top of the .NET framework, which seems to be gaining adepts these days).
It has a number of interesting features, such as weblog threading. That is, if the feeds you susbcribe to provide full HTML contents, SharpReader will match links betweek feeds (and provide you with a nice outline of those links).