The WSTC maintains a listserv for discussion, called WSTC Talk. To join this list, simply add your name and e-mail address to this form. A confirmation email will be sent to you. Click the confirmation link in that e-mail to join WSTC Talk. You can join or leave the list at any time.
This mail list is mostly for transportation issues, but any West Seattle related discussion is fine if people want to use it for that! There is no other peninsula-wide mail list currently and no other public transportation-focused e-mail list in the Seattle area.
The mailman page for WSTC Talk is here.
The WSTC Talk public archives are here.