Adobe
- Security alert notification service.
- http://www.adobe.com/devnet/security/security_zone/notification_service.html

Oracle
- Oracle security mailing list. Requires registration.
- http://www.oracle.com/technology/deploy/security/securityemail.html

HP
- Subscribe to HP Security Bulletins. Requires registration.
- https://h30046.www3.hp.com/subprofile.php?jumpid=in_SC-GEN__driverITRC&regioncode=NA&langcode=USENG&subs=ITRC

Red Hat Linux
- Notifications and advisories. Security mailing list subscription is on this page.
- http://www.redhat.com/security/updates/advisory/

Gentoo Linux
- List of security announcements and information on how to sign up to security mailing list.
- http://www.gentoo.org/security/en/index.xml

SuSE Linux
- All SuSE Linux mailing lists, including security alerts.
- http://www.suse.com/en/private/support/online_help/mailinglists/index.html

Microsoft
- How to subscribe to the (free) e-mail notification service that Microsoft uses to send information about security of Microsoft products.
- http://www.microsoft.com/technet/security/bulletin/notify.mspx

Apache
- Apache Week, includes security alerts.
- http://www.apacheweek.com/aw/email

Debian: Security Announcements
- Security announce mailing list for Debian Linux.
- http://lists.debian.org/debian-security-announce/

OpenBSD
- All OpenBSD mailing lists, including security alerts.
- http://www.openbsd.org/mail.html

NetBSD
- Security mailing list subscription.
- http://www.netbsd.org/cgi-bin/subscribe_list.pl?list=tech-security

Sun Security Information
- Includes subscription instructions for the Sun security-alert mailing list. Subscribe to this list to be alerted when security patches are released. Very low volume.
- http://sunsolve.sun.com/pub-cgi/show.pl?target=security/sec

SGI
- SGI® Security Advisory mailing list.
- http://www.sgi.com/support/security/wiretap.html