Your not so cheap ideas.

[enystrom8734]

Power switches - When placed, if a colonist leaves the room, they turn off the lights saving power. Or when they go to sleep they turn off the lights. Also allows you to control whether or not you want to grow any more food. Currently you can just toggle the light, but if you have a large room...

[GC13]

Like Huxi I also had the idea for a firefighting robot. It might be a bit complicated, but if you combined the behavior of a battery (since it needs to be powered while working) and a bed (where it recharges and is returned when "rescued" by a colonist if it runs out of energy while working) I assume the existing systems would work with it.

Anyway, some new ideas:

• Garbage pit: A dumping area with extra capacity that takes time to build.
• Reclaim land: Metal cost to turn the ground type into soil.
• Cultivate plant: Place a local plant onto the square.
• Bed ownershipâ€"Travelers: Allows you to make a hospitality suite. Travelers will stay the night, maybe tipping you for courtesy or joining you (I guess depending on the Happiness they get as a result of their stay?).
• EMT Training: Research project that reduces the rate at which people bleed to death.
• Firefighting Techniques: Research project that improves firefighting and makes someone less likely to catch fire.

[Lechai]

Meteor shower:

Random hits all over the map using the lightning mechanics.
Each hit has the explosive power of a blasting charge.
After impact, a few piles of meteorite fragments (metal) get spawned near the impact area.

Done
(Oh and i hope you all built underground)

[StarGazer]

Two ideas that should be fairly easy to implement (tho they shouldn't be too frequent, that would be way too annoying):

#1: Termite infestation: some termites infested the colony and are eating away at the furniture. Essentially the same mechanic as fire with maybe a bit lower spreading rate and limited to things like chairs, tables and beds. Spraying them with insecticide to kill them off (similar to extinguishing the fire). Maybe later add research for better insecticides increasing crop growth and improving termite killing speeds. Or cleaning stations to rid the colonists of dirt/bugs (aka showers).

#2: Raiders that aren't out to kill you but want to siphon off your power supply, tapping in to exposed wires/machines and then slowly (or quickly...) draining your power. Essentially code a raider that's  a huge energy consumer and hook him into the powergrid.

More to come! I'm so going to be loosing sleep thinking about these things...

[SpaceEatingTrex]

Thanks to Tynan for doing such a good job involving the community and responding on the forums!

Weapons:
i've said it before and i will say it again, tasers and other nonlethal options would be a great alternative way to capture raiders.   how about a rubber bullet or bean bag firing riot gun? sadly i think these would require a knocked unconscious mechanic.

I agree this is a good idea, but like you said the extra mechanics could be costly. An easy way to implement it might be to give people a "stamina/subdual health" variable that worked like health, but when it reached 0 they would be incapacitated instead of killed. "Stun" weapons could damage this.

As far as cheap ideas are concerned, I think it's still important for additions to have significance. For instance, adding objects that do nothing would be one of the cheapest things to do, but I think that would only hurt the game rather than adding depth.

Rough Terrain - Barbed Wire is an artificial structure that slows movement, should there be a natural terrain that slows movement?

Cat-like animal - follows colonists around.

Teleport Raids - raiders spawn in middle of player's base.

Turret Drone - Turret with Raider AI.

Giant Bones/Spires/Monoliths - map objects with no functionality but looking nice.

[StarGazer]

Another idea:

Scavengers: Some people/raiders show up trying to grab any metal deposits you haven't collected yet, you could then maybe choose to kill them before they take off or have someone convince them to join your group.

[SpaceEatingTrex]

Animals spawn food when killed - I've noticed watching LPs that player can bury Muffalo corpses, but other than that and psychotic animals there doesn't seem to be much interaction with wildlife. If animals spawned food on death it could make hunting a source of food. It also sets up for a future introduction of different types of food, like vegetables and meat.

Sims-style speech bubbles - Tynan has written a number of blog entries about game design, and in this one titled "The Simulation Dream" he mentions the effect conversations in The Sims series have on players. Should we use the same kind of thing when Colonists talk to each other, with a speech bubble and some image of the conversation topic inside? That wouldn't have to change any behavior, just display extra graphics.

Chemical/Persistent Fires - Fires that don't extinguish unless a colonist puts them out.

[BananaFromHell]

I think a building which will mine metal from inside the planet. This will be a great thing for the later stages of the game since you have mined all the metal that is exposed. And constantly buying metal from traders is not that handy since you can spend your money better on slaves or (the earlier mentioned) weapon traders

[huxi]

A "hidden" turret (researchable) that hides below surface until enemy units are well inside range - and then spring into action. It would need two radii - the radius it can reach with its weapon and a smaller radius that causes decloaking. This would help against enemies with sniper rifles... This turret type should be more expensive than the standard one.

[Jojomon]

Rattlesnakes and other vermin with any combination of the following fairly simple behaviors:
-create unhappiness de-buff when observed by colonists (like observing corpses, but not as traumatizing)
-quickly reproducing; at the start of each day, generate a random number from 0 to 2, if <1, nothing happens, if >= 1, spawn more vermin (thinking something like this: http://www.youtube.com/watch?v=IOwinLWrEIw)
-attack anything that comes too close

A variety of melee weapons such as clubs, metal pipes, spears that have a longer reach, etc. Could be fun.
Smoke grenades- non-lethal, but blocks line of sight. You probably wouldn't have to adjust raiders' behavior much if at all, they can walk through the smoke cloud or around it to regain LoS
Tear gas- also non-lethal, but exposure to enough of it could be incapacitating, and/or slow units down. And of course this paves the way for mustard gas, nerve gas, clouds of flatulence, who knows?

As for things previously mentioned, an abandoned building somewhere on the map sounds great, preferably with skeletons inside, also the possibility of an abandoned cave. Hopefully at some point they'd have prehistoric style cave paintings on the walls, depicting a muffalo hunt. Archaeology anyone? 
Hedges, ditches, and other "wall" types would be great.
I am also all for fire extinguishers as it gives something useful for your non-violent units to equip.

[Enjou]

A body armor system.

Basic body armor - low tech body armor, lowers damage from bullets but the wearer is a bit slower when moving due to the added weight. May degrade over time.
Power armor - Greatly reduces all damage taken by small arms, greatly increases melee damage, greatly decreases firing speed. Also faster at mining. Degrades over time but can be repaired with metal.
Kinetic shield - A high tech shield that completely deflects kinetic damage until it is depleted. Must be taken to a charging station once it is depleted.

Behaviors could be modified later to take armor into account, but it wouldn't have to be initially.

[Haplo]

A small idea to make raiders a little bit harder:

I think the raider alert, could be changed:
-From the beginning you don't get alerts that raiders have landed. Only when they are ready and start attacking you. (or not at all? Or only when spotted?)
-You can research some alert options and afterwards build a small radar dish or something else.
-Only when you build this (and it is powered) you'll get the alerts of raiders as it is now.

With this it is more likely to get surprised by raiders and they have a chance to slip by your disabled towers. 

[wqcoleman]

Here are some easy one I would imagine, might include artwork and modifiers:
- vaporators = (ala star wars fame), where you get a +x modifier on growing your farm (possibly improve crop yield or requirements as well)
- data cores (ala eve-online fame), modifier to research and either get them from mining (hidden lost artifact) or trade
- hovercart (ala dwarf fortress minecart) move mining resources automagically from x to y. setup routes (might be a bit more complicated than just modifier/art)
- derelict spacecraft parts for your colony - find a derelict spacecraft and strip it of parts like chairs, cabinets, flooring, and make a motley looking colony, for artful purposes
- alien technology - again, not really helpful in terms of modifier/easy implementation, but could be neat if you got something that would melt raiders that was found in some mine, trade or through some other means

if i think of others.. I'll add them..

[pyrojim3]

so i was thinking maybe as a large group of raiders land you could have the option to buy some mercs as friendly npcs's  to help defend your colony. you could put in a zone that defend and they would leave after the pirate raid. or some space cops as a random event just help or  at least some friendly npc's. not everyone in the universe want to kill you

[huxi]

I did search and although I found ideas that had the same name, my concept is slightly different.

Here is my super simple idea, a power switch.

When placed it conducts power and can be toggled on and off.

Possible use cases:
Creating backup battery banks that you can enable if power gets disrupted
Creating power grids that allow you to prioritize power in an emergency, i.e one circuit that disables hydroponic lighting when power is low and raiders strike.

Ideally such switches wouldn't have to be toggled on the map. It would be perfect if they could get a label and would also show up in a special menu/window with checkbox to toggle the state. Sounds very helpful.