With a bunch of refreshes, here's a probably incomplete list of what graphics are needed. (Not necessarily not made yet, just not implemented in the game.)
-HoloDetecter
-Acid Spitter
-Probe
-Predator
-Alignment modes, resurrect
-Spideroid
-Cyborg
-Buggy
-Symbiont
-Force-shield
-Blaster
-Tank
-Hover-Tank
-Drone
-Psi-Lord
-Psi-Warrior
-Alien
-Alien Hatchling
-Mutant Mount
-Fire Hound
-Tentacle
-Fire
-Laser Robot
-Slime
-Flying Slime
-Slime Beast
-Hovership
-Face Grabber
-Mutant
-Light-Sabre (soooo copyrighted already)
-Forcefield
-Alien Blob (is that what it's called? Didn't see it in the game)
-Fortress
-Subspace Beacons
This list is just for reference.