I currently use Bloglines, but the Firefox integration stopped working when Firefox 3 came out because it "doesn't provide secure updates." This is the integration that provides an icon in the browser when new feeds come in. Now that it's been a couple months, I'm re-evaluating if there is a better feed reader out there.
I'm currently using Akregator from the KDE project on Linux. I've tried many others from console clients to browser plugins but some are just ugly, others aren't very handy and most of them just showed very poor concurrency capabilities when you wanted to update more than 10 feeds so the browser or the whole desktop started to freeze during the updates. Regarding these issues Akregator was the best application I could find for Linux.
Marco [ September 05, 2008: Message edited by: Marco Ehrentreich ]
Sorry, I'm currently using Firefox 3 but I didn't test any RSS plugins since this version came out... The best browser plugin (in my opinion) I've used with older versions of firefox was "Brief". In contrast to others this plugin worked reasonably fast when updating feeds and didn't freeze the browser for seconds. And it's obviously available for Firefox 3, too.