I always have a central spiral ramp around a 11x11 (or 21x21 when I want to go bigger) hole that goes down to the caverns and gets expanded to the magma sea when I find the time. Above it there's a square tower to the top of the sky. So basically a drop from very top to very bottom to fling down prisoners or annoying nobles with all the dwarves watching. See, there goes the mayor that wanted a platinum bed and slade cabinets in his bedroom... who's next?
I don't like building fancy tombs. Dwarves who do especially well get nice rooms with matching furniture to live in, but in the end, everybody goes into a big square room full of simple rock coffins.
Another quirk are the prison cells. Normal dwarves live in 2x2 to 3x3 rooms with smoothed walls, a bed and a cabinet. Prisoners go to 3x3 cells with masterfully engraved walls and floors, masterwork bed, table and chair and stockpiles for the best food and booze. When my legendary armorsmith goes to jail for not producing platinum crafts (with no platinum available, not even through trade), I want him to have some fun there and not die of thirst or madness.
And I love circular dining rooms. It doesn't matter if my dwarves need a dining room at all, I got to build one. The biggest one so far was about 50 tiles in diameter and 3 levels high with big columns and balconies, every tile engraved with the history of the fort (and the occasional cheese or purring maggot), a small lake in the middle and room for 200 dwarves at least... in a fort of 80. Like a cathedral of booze and plump helmet roasts.