The recent things I added to my house was a water elevator that leads to my roof, so I can grab my bow and shoot skeletons, creepers, spiders, etc. I've also added a secret door, that leads into my basement. My basement organizes my treasure, food, building materials, etc. I've also added a little obstacle corse (for fun) just so if its night or something and i dont feel like going outside to mine or fight, i just add on or complete my obstacle corse.
I did an electrical light system with two on/off buttons in different places, using a flip-flop in the basement. It was useless at the time due to the low light intensity from redstone, but it would work with pistons and glowstone. However, you have to design your house around the circuitry due to the size.
My house in my old world had a secret door down to my mines and underground farms. Also had a library, full of bookshelves. Waiting on player written books to make a real one, though...
Not in my house, but I had an underground railway connecting my two bases across a continent (well, large island, but it was a couple hundred meters from base to base. Long enough to eat its fair share of iron).