Make a glass tower wrapped around a tower of lava dispensers to make a timekeeping device you can use from however far away you can see it.
Another idea is a pixelart display powered by redstone to swap between different images (like those mechanized/electronic billboards you see in RL).
Perhaps you could build a secret lab in similar style as Raccoon City from Resident Evil. It would have a "disaster mode" circuit incorporated that might open up the killing chamber so mobs could wander freely--allowing you to hunt them down.
I suppose it's a bit late to suggest it now, but I'd recommend digging it in a circular shape and having a circular staircase in the middle that branches out into a number of different rooms for different purposes (chest room, farms, sheep pens, nether portal, brewing room, smelting room, etc) all on different levels. This picture doesn't quite do it justice because this was an early version of it, but this is sort of what I'm suggesting. This was done by someone on my server a couple years back.