FFW Small Markets -
Both edited by C. Hope Clark, founder and editor of FundsforWriters.com, a website, family of newsletters and ebooks about incomes streams for writers.
New Zealand Book Council E-newsletter - http://www.bookcouncil.org.nz/Readers/Newsletters/Information.htm
Newsletters from the Victoria University centre of the International Institute of Modern Letters (not strictly monthly)
Helen Heath's Monthly Newsletter (recently signed up so haven't received first issue yet)
What writing related e-newsletters do you read and recommend? Please share via the comments section.