I come across more and more blogs, especially since I started using Twitter to find them, so I can't mention them all, but here are three I really like. Bookwitch has interesting posts herself as well as two useful features - lists of interviews with and links to the blogs of many famous children's writers.
If you want recommendations from young readers themselves, try these two. I'm impressed with East Renfrewshire's Teenage Book Blog, and The Books I Read which is by a 9-year-old boy living in London who shows amazing review skills for one so young (or for anyone really).
For other blogs, I will usually post here about interesting information picked up or re-tweet it on my own Twitter stream rather than the library one which I keep for more general announcements (including occasional reminders that this blog has been updated).
There's a useful article here on children's book blogs with links to 10 "you can't live without".