I'm in for the Space Monster. As a former player of MOO2, having space monsters really adds the spice factor to the game. I would love to see it in GalCiv2 too.
monster types, derived from MOO2
Space Dragon - 8 phsors Eye, 1 Dragon Breath
Space Amoeba - Caustic Slime
Space Hydra
Space Eel - Plasma Flux, Lightning Field
Space Crystal - Crystal Ray, 3 Death Spores
Guardian - 2 Death Ray, 10 Particle Beam, 2 Plasma Torpedo, Achilles Targeting Unit, Battle Scanner, Inertial Stabilizer, Multi-Wave ECM Jammer, Automated Repair Unit, Hard Shields, Lightning Field, Rangemaster Unit
But since we're talking about galciv2, it should be a bit different, to be more original right?
Space Shark, already mentioned... in galciv1
Sentinel, sort of like a Guardian, but it's humanoid, has lots of powerful attacks.
Space Bees/Bugs - attacks in huge numbers/swarm,
Moon Monster - Monster that looks and behaves like a moon, floats around a planet, but will attack anything that goes close to it.
Ghost Ships - This adds some horror element to the game in which unmanned lifeless floating battle-scarred, damanged spaceships come to lights up to attack the life-manned spaceships, this encounter should extremely be rare...
Space Leech - feeds on ships electrical energy, will attach itself to ships to drain energy off the ships, while ship's shield, hp deteriorates.
Space Siren - these space monsters have an irrisistable sound frequency that hypnotizes captains and sailors into navigating close to it, causing the ships to crash land into a 0 class dead planets.