Physhare - An unmoderated listserv dedicated to precollege physics education. Archives since 1991 are searchable.
PHYS-L - Email list for physics educators with about 700 members and typically 5-50 messages per day. Online archives (for posts since 1996) and membership interface available.
TAP-L and PIRA - Frequently asked questions regarding the physics demonstration-related listserv TAP-L (Teaching APparatus) and the affiliated organization called PIRA (Physics Instructional Resource Organization).