"Out and Out Exploits" (these are things that clearly aren't functioning properly but can be used to your benefit)
-Danger rooms (You can train up a squad to legendary absurdly quickly with virtually no risk.
-Quantum Stockpile (Endless storage in one square)
-Atom Smasher (crush nearly anything to dust, though it can be useful to help mitigate FPS a little)
-Stealing from Caravans (only an exploit in that there isn't any real notable punishment for doing so right now, so far as I can tell)
"Things that aren't exploits but are far overpowered"
-Dodge traps (make a one space wide hallway with pits on each side and fire at enemies = win)
-Endless hallway of traps (not a bad thing really but given how easy it is to build traps its overpowered)
-Cage traps (seriously, capture just about anything in a wooden cage and keep it there forever)
-Walls + Drawbridge (keeps out 99% of enemies that you can just plink away at with bolts until they leave)
-Magma (Now that you can get it very easily in any map its a bit overdone, IMO, you can infinitely power forges to make metal objects with no cost)
-Steel (granted its a bit hard to get depending on where you are but once you have it short of 'digging too deep' you basically win
-Farms (I hesitated to put this one up cause technically they are pretty overpowered, one good sized farm will feed just a huge amount of dwarves and requires very little work to build or keep going.. That said depending on where you are getting food elsewhere may be extremely difficult to impossible so you don't always have another choice)
I'm sure there are others.
So far as I know nobody really cares which of these you use though since its a single player game without a score or anything. I mean if you break them all out you certainly aren't offering yourself much of a challenge but why anybody else would care is beyond me. I feel about the same as I feel about "God Mode" cheats in single player games, I would never do it cause to me the challenge is the point, but if others do more power (literally in some cases) to them.