Well I didn't get a chance to post one yesterday, so I come baring two today.
Orbital Strike Cannon
Any location with a direct line-of-sight to the skybox can be targeted. A couple of seconds after the target has been designated, the cannon fires a high energy pulse (Like a giant version of the pulse rifle) at it, annihilating anything nearby.
Dretch Cannon
A small globe-shaped structure which can be built on walls, floor and ceiling. A dretch can climb inside it, as a granger can climb into a hovel, but then using the mouse to aim and fire, the dretch can launch itself in any direction.