I'm afraid I'm too obsessed with some form of automated defense buildings, like turrets, to think of anything else that everyone else had suggested.
but I would like turrets, as well as a small or reasonably big handful of new gadgets, blocks and buildings to piece together with wiring to make some complex and visually pleasing constructions.
I can suggest something like a block that works like a magnetic force, like when a block is alternated between two polarities will push or pull the closes thing to it, or either in front or behind it.
Otherwise, I'm still waiting for turrets to happen, even if Red stated they won't happen. I think it's possible, people are too busy trying to predict how the dev's want it and try to botch any turret ideas ASAP, rather than find a way to make it work. Like make it have pitiful damage capabilities, limit to how many can be on one wire network, have the multi-directional aiming capabilities and give it some ability to lead it shots towards enemies. To top it off, it always aims for the closest thing to it; even if its got one enemy to work on, it'll break away to fire at anything that got recently close, overwhelming it. (and yes, Terraria:Otherworld will have it; It's not out, I don't have the cash yet to buy it, and the argument gets as old as a loaded question.)