Hmm..
Artillery Emplacement - Large (like 4x4 or something, maybe have a smaller version as well), needs open sky, and fires large shells with a mining charge-type explosion. Would need someone or something to spot for it (If that's not too hard to do), and can't fire within a certain range. Would cost a lot of metal and have a large power draw, and wouldn't be terribly accurate.
Also, as an idea (Even though it's not cheap, time-wise), perhaps it could be set to fire on pods (and other things) entering the atmosphere. Wouldn't be the best at it, but it still could take out, say, 15-25% of a raiding party at best, which could mean something. As a downside, it would prevent you from trading due to shooting down the drop pods full of stuff.
Manned Turret - Lesser power draw, about the same metal cost, and needs to have a drafted colonist to man it. Would pull from the skill of the person. Perhaps have it act as partial cover, too - The turret or the person manning it can be hit.
Defense/Safety Zones - Set like a Home Zone, these would still have colonists fighting fires (More urgently in the Safety Zone), but in the case of a raid, colonists assigned to a defense zone (Or with the 'Defense' job/setting active) will man their stations, taking the best cover they can, manning turrets, etc. If raiders make it into the Home Zone(s) (or just get into the Defense Zone, former might be better), all colonists will attempt to either retreat to the Safety Zone (And block the doors up) or, in the case of a 'Normal' mode (Thinking it could be something toggling between 'Defender', 'Normal', and 'Non-Combatant') act like those set to defend would. It would be a way to be able to set up defenses without having to worry about drafting people all the time. They would (hopefully) be smart enough to avoid grenades, and if the metal is available, the colonists that are building would try to re-build defenses (Or just sandbags/walls) after the attack. The way I see it, it's using the Raider's combat AI and limiting it to a zone.
Herbivore Inertial Generator - Just a treadmill that colonists would drag Muffalos onto, keep them fed, and it would generate some power more or less continuously. You could use a re-named variant of the 'Prisoner Treatment' menu thing to set how well they treat it and how much power it makes. Downside is that if that muffalo gets free and angry.. Well, it's probably close to things that can be blown up.
Mass Grave - The same size as a dumping ground (or maybe just 2x2), can hold a larger number of corpses. Can possibly also be used as a fall trap, but that'd probably be a bit expensive.
Food Dispenser Upgrade - Takes a bit of research, makes the dispenser use more food per meal (possibly), as well as some spices (A different thing for a growing zone), but it's a cheapish way to make a standard level of food that people don't complain about nearly as much (if at all). Produces Ration Paste ("Some spices have been added. It is now mostly edible."), adds a production option in all Nutrient Paste Dispensers.
Item Transport Tube/Item Transport Receptacle - A cross between a stockpile and power lines, only bulky. Have a 2x2 area where colonists can put collected items which, if connected to a pump (For the tubes to have suction), the pump is powered, and there's a tube leading through the pump to the Stockpile, it will quickly transport the item there. Perhaps there could be a range limit on the pumps (Maybe not), and even a slight need to have the Stockpile and Food Dispenser connected by pipe to keep it topped off.
Can then lead to 'Fun' storyteller events ("A boomrat was in the wrong place at the right time and was sucked into your stockpile! It gorged itself on the food within." -15 food, "One of your item pumps has become clogged, and it sounds like a Muffalo is stuck inside." Damage/shutdown of the pumps along a line, won't re-activate until the blockage is cleared.)
Rock Crusher - Has a 3x3 storage area for rocks (is 5x3), destroys the rocks or turns them into a very small amount of metal/other resource or gravel. If gravel, then that could be a tile that you could put down. Slightly faster movement (?), makes a nice crunchy shifty noise. Possibly even using gravel as a resource for an alternate sandbag?
Organic Material Reconstitutionalizer - Can be used to 'store' corpses in, alternate food dispenser. Dispenses 'Green Goop ("It doesn't smell that bad.. But there's something that feels off about it. Food's food, though.", causes a happiness loss between raw food and nutrient paste, slight fear increase).
That's all I've got for now..
