I had an idea for a new weapon/item. I don't know precisely how to categorise it, but it would probably fall under "miscellaneous". From the discussion about stealth and sight ranges it struck me that one of the most perceptive alien races also has highly developed hearing,
Ortnok - "The eyes are covered with surgically-implanted lenses that improve the Ortnok's already excellent vision, stretching it into the infrared spectrum. The ears consist of a series of small cavities, three on either side of the head, which are surprisingly large and well-developed. Given the evidence we must conclude that Ortnoks have acute hearing..." (
http://ufoai.ninex.info/wiki/index.php/Aliens/Ortnok)
It struck me that they might be sensitive to some sort of sonics. Now I'm not talking about "sonic guns" or anything, but rather a much simpler (and arguably more effective) device that would emit sounds in a frequency inaudible to humans, but at least very distracting to the aliens, and at best actually painful and disorienting. The Sheevar, with unusually large quantities of bone in their skulls might also be vulnerable to similar frequencies.
This "weapon" could take the form of an add-on to the drop-ship (e.g. a large transmitter that screams these frequencies across the battlefield), or perhaps a series of transmitters on poles that soldiers plant into the ground as they go. Hell, if you want to be slightly tongue-in-cheek about it you could even have soldiers trotting into battle with boom-boxes playing, "Yodelling Hits 2030", or "The Best of Bagpipes". I'd call the item a "screamer", because that is basically the effect its trying to achieve. It's difficult to concentrate in battle with someone screaming in your ears all the time.
This could even develop into a whole tech branch with sonic staves (although I'd prefer to visualise this as a sonic naginata) - a weapon that emits a pulse of sound designed to resonate with alien physiology to bypass their natural defenses, new flash-bangs - designed to emit frequencies that are more effective against a wider range of aliens, and eventually possibly even crystalline rounds designed to penetrate skin and then emit a sound pulse that is amplified and damages internal organs, before shattering and inflicting a little damage (the plus with this round is that bone could also carry the sound to the auditory nerves and have a stunning effect).
This sort of idea has been around for a while, I think the military investigated the idea back in the 60's, Kate Bush wrote a song about it. ... oh, and there's also, "Day of the Killer Tomotoes", but I don't think we want to go there.