I'd like to make a few trap suggestions. Caveat: I've read this thread, and did a search of other thread topics, and didn't see any evidence of these specific suggestions before, but I could easily have missed them:
1, Log traps: Should work outside, replacing boulder traps. Boulder traps might still work outside, but I think they should only be placeable alongside other stone, either natural rock (somewhere on the mountainside), or stone construction. Logtraps would be placeable anywhere outside, and would come in the "single log" and "double log" varieties.
Logtraps and other outside traps might still be useable indoors, ofcourse.
Vermin trap: Your typical boulder trap, just replace "boulder" with "giant wasp's nest", or "fire ants", or "cave spiders" or "scorpions" or "vipers", or "shrews", or "badgers"
,or (my personal favorite) "thousand upon thousands of hungry fleas". Could even be useful to load it with an angry housecat or a skunk. Definitely an outside trap!
Punji trap: Another outside trap, but requires wooden stakes, instead of wooden logs. May have multiple stakes, and would work like a weapon trap.
Pitfall trap: Another outside trap, must be built over a channel. Only activates for creatures larger than a human, and can either function as a cage trap (if it's empty and only 1 square deep), or as a damage trap (if it covers something dangerous, like water or spikes, or if it's several Z levels deep)
Alternative: Muscovite--Not always an intentional trap, at times just a dangerous terrain feature, it could still be utilized or taken advantage of, by dwarfs. Sheets of muscovite could be used to make pitfall type traps that would blend in to other stoney/underground terrain, as opposed to pit traps, which would be designed to blend in to outside features. Muscovite would also break under the weight of heavier creatures. Unlike pit traps, your dwarfs would have to actually locate a mineable source of muscovite to use this kind of trap.
Snare trap. Functions as a cage trap, but only activates for creatures human-sized or smaller. Must be built alongside a tree.
Jaw trap. Classic "beartrap" type component. Traps the target like a cage trap, but also does piercing damage.
Pneumatic trap. Trap that sprays a liquid or powdery substance. Might be flammable (coal dust, oil, what have you), or acid, or poison, or some sort of liquid creature, like a slime, or water (in sub-zero temperatures), or powdered sand or glass (sand would be uncomfortable and blinding, while glass might cause damage over time, especially if it got under heavy armour). Bauxite mechanisms might even spray liquid magma, although this would likely be a 1 use trap.
Door Traps:
The Guillotine Door. This is a door that, if it isn't opened in the correct (counter-intuitive) way, it causes a blade (glass or metal) to fall, cutting the attempting opener lengthwise, in gruesome fashion.
The Portcullas Trap. A spiked door either falls or swings sideways into the victim, doing damage, and then subsequently blocking the hall, as a locked door. Requires a gate as a component.
The Door of Amontillado: This is a door, which if opened improperly, would cause a stone block to fall behind the opener, trapping them between the locked door and the block. Fun with water, magma, murderholes, etc. could then ensue, or you could just wall that door off and leave the victim to mummify.
Double door down: This involves two associated doors in a row, with the first one trapped to fall on the victim, as a stone-trap, if opened improperly. Triggering the first door locks the second.
An alternate to this is 2 (or more) associated doors, that when 1 is opened, a stone block slides down and blocks the other door (s). This can either be used to seal off a door in *front* of the intruder(s), or seal the door(s) off *behind* them, forcing them to continue forward.
False door: This is a door that is never intended to actually be opened. Opening it, or attempting to open it, *always* triggers a trap. Kobolds and the like would still have a chance to detect the purpose of this false door.
Keyhole trap: This involves a door with two or more keyholes. Only one is the right one. Failing to pick the right one, or choosing to pick a false one, triggers a trap. This can involve crossbow bolts, poison needles, sprays of acid, etc shooting through the false keyhole, or the setting off of various other traps, or the door's proper lock may simply fuse solid.
Contingency trap: A trap that is only primed if a prerequisite is met. Stepping on the wrong square of a floor several levels up or down, opening up the wrong door in another part of the fortress, etc. causes the trap to become active. Otherwise, it's harmless.
Shot trap: This is a simple spring mechanism (as simple as a tree limb), attached to a tightly packed bundle of metal needles. Extremely short range, and worthless as a standard weapon, it nonetheless would have a high probability of doing *some* damage, and ofcourse, makes a perfect poison delivery system against unarmoured enemies. Alternatively, a very similar trap could be loaded with broken glass, sharp metal discs, wooden splinters, crushed rock, or lead spheres.
Pertaining to trap components:
It would be nice if we could make use of poisons in the game, especially by tipping wooden spikes used in traps with them. Tipping them with glass points, or just glueing crushed glass to the pointy ends (or to other wooden trap weapons, like giant hammers), would also make them quite a bit more deadly.