Enchanted Moondial (not really a mechanical item), or some sort of statue/switch/potion that can be activated to make it the start of night time!
Larger doors that can be opened and closed with wiring. Trap doors that open and close(I realize that activators can do this, but having an item that looks like a trap door, that people know may open up if they step on something or press the wrong switch.)
Doors that require a code to open, like when you right click it, a number pad pops up and you must input a 4 digit code to open it successfully. When you put in in initially, you'll be prompted to set the code. These doors are unbreakable, and can only be removed from their open state. When the door shuts, it locks it. Optionally, a wrong code could trigger a wiring signal to set a trap.
An actuator type item that makes it impossible to mine the block it's placed on. It must be used carefully! But as a precaution, there's a pick/item that will let you remove these blocks, but it's very slow and takes many hits to remove them.
Of course, statues that can summon most of the mobs, instead of just a few. Maybe also invisible statues that summon mobs, you can only see them when you are holding a wrench/wire cutters and they look transparent, like when placing furniture.
A second set of heart and mana statues that drop large hearts and large stars, that do double the healing/mana recovery. Of course, the current mana statues could be nerfed to 50 mana recovery to accomodate larger 100 mana recovering stars.
If I think of more, I'll be back of course!
Thanks for everything already! You guys are the best at listening to your audience!