What are the current blogs on R? What do they cover?
What makes a good blog on R?
Of course different readers look for different things, but for me a good blog on R:

• Provides a Gateway: The blog discovers and shares useful external material and explains why it’s useful
• Provides A Forum: The blog raises important issues and topics. Better yet if the blog can initiate debate.
• Generates Original Content: In particular it is useful if it can teach the reader how to do something. Better yet if the thing taught is of general appeal and is taught clearly.
• Posts Frequently: E.g., 2+ posts per week.

Blogs on R:
UPDATE: R bloggers compiles many of the blogs on R into a single source and is probably the best place to find a list of Blogs on R. You can also subscribe to all of them through R bloggers.

These are some blogs on R to which I subscribe.

• REvolutions: A blog devoted exclusively to R. This is probably the best blog on R currently around. Among other things it has interesting applications, references to resources, and interesting assorted tidbits. 
• Statistical Modeling, Causal Inference, and Social Science: This is probably the best example of a blog in the social science statistics area. It has a large readership and good discussions in the comments. Only a small percentage of posts are on R; many of the posts reflect the author’s interests in political science. For R stuff, check out particularly the category Statistical Computing.
• One R Tip a day:This blog is devoted to R and has lots of interesting examples.
• Decision Science News: Sometimes has posts on R.
• Planet R: This is a meta-blog that pools subscriptions to a large number of feeds related to R.
• Andrew Redd
• Romain Francois
• Gregor Gorjanc
• Quantitative Ecology: 
• Blogistic Reflections
• Getting Genetics Done: R Tag
• Of course, there’s my own blog. with the R tag.