Alien that shoots pheromones out of his body which attract bees (needs hives nearby).
He could then shoot a ball which the bees will chase.
Suicide bomber alien that doesn't do direct damage but gives emp blast which temporarily jams defensive structs (and arm/medi?)
Type of Goon that can ski (like in Tribes) by holding space. Pounce, slide, drift around corners
Sneaky alien that can attach to a human's back without him or anyone noticing it. (seems like a bad idea, but kinda cool).