The Internet is a treasury of resources for writers. Here are a dozen newsletters that I think are particularly worthwhile. Some you can subscribe to the RSS feed or by email. Others you can read on site.
Ralan's Market Report
Covers SF and Fantasy as well as a few others. Not automated. You must send an email to firstname.lastname@example.org.
Cynthia Sterling Market News
Covers fiction markets on a weekly basis. Automated so send blank email to:
Morning Coffee Newsletter
Working Writers Newsletter
Book Publishing News
Horror Fiction News
Food Writing Newsletter
Poets & Writers: Tools For Writers This page has an eNewsletter registration at the bottom.
Angela Hoy's Writers Weekly includes warnings about deadbeat publishers.
A good writer must always have two goals: work to be a better writer and know what's going on in the marketplace.