Okay, my first post on this topic got corrupted.
Known turrets:
- Machine Gun
- Rocket
- Scatter Laser
Plausible turrets:
- Plasma
- Rail Gun
I think it would a really cool addition to have a stun gas / stun grenade / stun bomb / thermal shock bomb (whatever you want to call them this time around) launcher turret. It would come in handy when you need to stun aliens, especially ones that unwisely grouped together on a terror mission. It makes realistic sense, given that riot control vehicles (read: armored vehicles like the Hunter) have tear gas launchers.
For balance issues, you could make it only have 6-8 shots.