I've had a couple of companies brought to my attention recently that would make good additions to the list. Thanks, Dorit, for letting us know about Six Red Marbles.
I also received an email from Ken Yablonsky inviting us to check out MathQueue, Inc. "We are a math-specific editorial company who has done recent work for Pearson, McGraw-Hill, and HMH. We have a good rapport with Words and Numbers, Element, and GGS. We would love to be added to your list of Education-Related Publishing Companies." Ken says the work is slow right now, but occasionally they get swamped and will keep this blog in mind when looking for freelancers.
Happy weekend!
Laura