What are the best public places to discuss existential risks?

My list in order of quality:

Useful:

Lesswrong.com

https://www.facebook.com/groups/ExistentialRisk/

Semi useful:

http://www.longecity.org/forum/forum/360-risks-survival/

https://www.facebook.com/groups/lifeboatfoundation

http://effective-altruism.com/r/main/

Almost dead now:

Lifeboat foundation mailing list - almost dead now, but had good discussions before

http://www.forumlog.com/nanobiotechnologyspace/index.php

https://www.reddit.com/r/ExistentialRisk/

Special:

http://forum.arctic-sea-ice.net/index.php/board,25.0.html

flutrackers.com