Well I've been extremely busy the last couple of days, so you get three today, aren't you lucky?!
Head Cannon - The last resort for a human. Worn like a helmet, upon use it irradiates and launches the player's head, killing the player and anything that the head hits.
Shark - An alien class which travels just below the ground, with only a very small portion of it's body exposed, but when attacking it leaps upwards out of the ground, killing anything in it's path.
Energy Shield - A Human defensive structure, it projects a quarter-spherical, blue energy shield directly infront and above itself, which vapourises any alien which tries to pass through. It does not vapourise humans, although they are unable to fire energy weapons through it. Alien ranged attack can still penetrate it, though.