EMCrit blog: if you're not following this and the podcast, stop what you're doing and catch up. http://emcrit.org/
Other Things Amanzi: not EM, actually from a surgeon in South Africa, but it's the best medical writing on the internet http://other-things-amanzi.blogspot.com/
Life in the Fast Lane: another Australian EM and critical care blog, pretty high volume but with a terrific weekly summary of the best of the other blogs, including most of the above http://lifeinthefastlane.com/
Oops! I don't know how I left that one out. It was a recent find for me but an awesome blog. I just really like the way that dude thinks. He's like an Australian Scott Weingart.
Less high-yield than some of the above, but among my favorites:
I'm surprised that StorytellER doc didn't get mentioned. Lovely writing. He's taking a bit of a break at the moment, but I do love the posts. http://storytellerdoc.blogspot.com