-- Switches back to default, General channel.
-- Intra-party chat
-- Intra-cabal chat
/whisper <Case Sensitive player name>
-- Private communication between two players
/w <Case Sensitive player name>
/invite <Case Sensitive player name> -- invites player to join party
/friend <Case Sensitive player name> -- Invites player to join friend's list
shift-leftclick with mouse to share item detail screens in chat channels.
If you know of any others please add them in the comments.