Mass grave rooms. Depending on the fort I'll give them coffins, then when every tile is filled with remains/coffins I either seal the room off or if possible I collapse something on it, pour magma in it, make an obsidian cast, ect.
Sometimes I'll make epic tombs for uberdorfs though. Once in d40 I had a champion who got an artifact elephant bone helmet that I planepacked into a ridiculous amount of wealth (around 3 times that of the rest of my fort combined), he was originally a legendary engraver, also got to be a legendary axedwarf, wrestler, shield user, armor user, ect. as a champion. I had an eight champion military and he was the leader, he had something like 500 kills on goblins and later handled an entire frog clown funhouse singlehandedly. Once I got funmetal the king came and *GASP* it was a goblin leader of DWARVES! So naturally my champion led the dwarves in a rebellion against this false tyrant, chaining him in the funhouse (because of a hilarious bug that treated non dwarven rulers as livestock) and claiming the funmetal throneroom for himself and his wife, who was also a quad legendary champion. All nobles were executed on sight other than the dungeon master and philosopher, the champions of the military became the new lords and ladies of the fort.
He eventually died considering that fort ran for like 80 years before I ended up abandoning due to lag, a lucky goblin arrow to the head ended up killing him. He got a 3z level 8x12 tomb full of bauxite statues decorated with rubies, a masterwork bauxite coffin, bauxite floors, (he liked bauxite and cows), magma channels for flavor, the entire room covered in masterwork engravings, mostly flux layers. He had two platinum cages with bulls flanking his coffin and one tile of magma directly in front of his coffin that was below a shaft leading up to the goblin stasis chamber, where I had a very large goblin cage stockpile. I kept most goblins for entertainment/training purposes but all archers captured after his death were immediately pitted down the shaft into the magma to appease him. His masterwork funmetal armor was placed in a bin behind his coffin, but the elephant bone helm was taken up by his wife. She never died but if she did she had a tomb full of cats, cobaltite furnishings and waterways across the hall waiting for her.