This post from the "Master in History" blog identifies 50 of the best American History Blogs, broken into the categories Colonial, Revolutionary, & Early Nation; Civil War; Other Military History; Economic; and General & Political.
I've selected only a few as examples to feature on this page...
The History Blogging Project "aims to...provide training resources that will enable postgraduate historians to create, maintain and publicise a blog on their research."
"...Through the development of an online collection of how-to guides, advice and examples taken from current history blogs, the Project aims both to inspire postgraduate historians to blog and to challenge existing bloggers to think about the ways in which they share their research with a range of different audiences."
"At the same time, the Project aims to create a forum in which postgraduate historians can network and publicise their blogs."
(The History Blogging Project is supported by the Univ. of Oxford, The History Lab, and Roehampton Univ. Description taken from The History Blogging Project website.)