There are several active blogs on market design. Two of the best are:
1. Al Roth’s (together with Peter Coles’) Market Design blog. This blog started in 2008. It is especially strong on matching market applications, such as kidney exchanges, school choice, and hospital-medical-student matching.
2. Noam Nisan’s Algorithmic Game-Theory/Economics blog. This blog started in 2009. As the name suggests, the focus is algorithmic game theory and economics. In my terms it is market design with a computer science spin.