As RSS becomes more common, and my news sources become more plentiful, I’m increasingly relying on a news aggregator for information management and consumption. For the uninitiated, here’s a definition I wrote a while back:
News aggregators (sometimes called RSS aggregators or news readers) are a new category of software that enables users to view RSS channels quickly and easily. A news aggregator, often hidden in your Windows taskbar, periodically checks each RSS channel to which you are subscribed to see if new news items have been published, and displays the results. Typically a news aggregator only shows the title and synopsis of a news item. By clicking on the item in your aggregator, you can then view the complete item in your Internet browser.
In a couple of years, this technology will be commonplace in Windows (in IE or Outlook, or both), but until then I’m using an aggregator. Thus far I’ve been using the free but simple SharpReader. It’s nothing special, but it gets the job done. I do feel like I’m missing some bells and whistles.
What aggregator are you using? Why? Here’s a list of the more common ones. My one requirement (for now) is that it be client-based, as opposed to Web-based. Unless a Web-based aggregator is really kick-ass…then I might conisder it.
DarrenBarefoot.com 
I know you mention no web-based aggregators, but for me the only choice is http://www.bloglines.com
They are constantly updating the software with new features, offer a desktop monitor for it, and I can access it anywhere without having to download software. Plus, if I ever do decide to use a client, I can download my feeds.
I use awasu (www.awasu.com) which seems more feature rich than SharpReader. However the free version of awasu does have an annoying pop-up which almost tempts me to buy their commercial product (at the low price of USD$15).
I could not agree more with Nick – bloglines absolutely rocks – i love it
BTW, the excellent ‘Evolution’ application from Ximian has RSS capabilites. This started off as an outline clone (in appearances only I must stress) but has surpassed it already.
I like getting news via e-mail so I use BlogStreet’s Info Aggregator as an RSS to IMAP feed. Bloglet isn’t bad either, but it dumps everything into a single message, which may be a plus or a minus depending on your personal preferences.
rss.blogstreet.com
http://www.bloglet.com