the big ones would be juxtapoz and wooster collective and then theres fecalface, arrested motion, etc and a lot of smaller blogs. if you go to juxtapoz or wooster they have tons of links on the side to sites like that
Revok's blog features some of the top graffiti-artists around the world, as well as formal artists whom either have gallery shows at Known Gallery or have an inspiration on him. This post right here is a great read!
This is our blog, from Chicago. Can't say it's a popular one (would like more traffic) but we add stuff weekly. You can cop gear in our store too. If you're in Chicago I deliver. Subscribe if you get the time. http://theblog.momentumarttech.com/