Blox0r, advertises itself as "The best online aggregator ever!" It's an AJAXy feed reader that uses a classic Outlook three-pane interface. On the left is a list of feeds you're subscribed to, a la Bloglines, and on the right are two panes, one for headlines and one to show the stories you click on. The default mode takes you to the actual web site so you can read comments and so on, the Preview Summary mode will show summaries of all of the recent stories in a particular feed. It has most of the features you expect from a web-based feed reader and a few more; it's open source, so you can download it, tweak the code, and run your own aggregator service if you want.