One blog that I read quite regularly is the nearly infamous Slashdot. It is wildly popular, with many thousands of people reading it daily. The content is composed nearly entirely of links to advances and news items in the tech world. While there are many new posts per day, with an average I would say of about a dozen new entries per day, the bulk of the content on the site comes from the comments from visitors. The comments are interesting in that they can be nested, making reading them more like a web forum than a standard blog.
The emphasis on the community aspect is one of the largest draws, and is especially evident in entries like this one from today, in which someone asks the readers in general for their opinion on a particular topic, in this case about whether the people who find bugs in software should let everybody know, or only the writer of the software. This allows for many people to voice their opinion on the topic, and opens up new ways of thinking about the idea.
As an example, I would definitely say the Slashdot is a blog that has done it right, and continues to be strong.