Blog Bridge (http://blogbridge.com/) is my current favorite RSS aggregator. It's a Java program, which means it runs on any computer system (that has Java) and it looks really nice. As you discover web sites that you want to track (and publish RSS feeds) you, find the URL of the RSS feed, click on the "Add Feed" button, provide the RSS URL to the dialog, and then the program takes it from there keeping you up to date on new postings on that feed. It organizes the feeds into groups they call "guides", and I use the "guides" as a topic category. It offers "feed discovery" that appears to look through the links in a RSS feed for other sites that themselves have RSS feeds. Hmm... I just tried that for the first time and it looks like a quick way to get totally swamped with news feeds.
NewsInABox (http://www.newsinabox.com/) I've never used because it's a windows-only program. I just looked at the site and see that it has an interesting idea for presenting news feeds. It makes the window look like a news paper.