I can’t believe I actually missed this website out, but better late than never! SEAMEO-SPAFA is the Regional Centre for Archaeology and Fine Arts under the Southeast Asian Ministers of Education Organisation (SEAMEO).
SEAMEO-SPAFA’s objectives include promoting cultural awareness and appreciation of Southeast Asia, particularly in the fields of archaeology. They have a good list of publications, including the SPAFA journal which is published three times a year.
I’ll be placing a link to SEAMEO-SPAFA in the links section, where you can find a list of other online resources in Southeast Asian archaeology.