In my most recent game I've been keeping an in-character journal, as if it were a one-person bloodline game. I've taken to writing one of these myself every year, but it's a pain. What I've been tracking:
Population
- Civilian breakdown by job (e.g. 6 brewers, 2 strand extractors, etc.), including 'baby' and 'child' as jobs. This past year I had a growth of 26 dwarves but only about 3 of those were adults.
- Military breakdown by squad, listing their weapon type and each dwarf by name so I can more easily keep track of those badasses who've made it through x sieges and y titan attacks.
- Nobles/officeholders
Wealth by the categories displayed on the status screen
- Food/drink by category
- Coins by metal type - they're useless, but I do so love having a giant horde of them on maps where I've got 20k gold ore lying around.
- Bars by metal type - it turns out I had about 1000 bars of precious metals and alloys gathering dust. Clearly it's time to chuck the stone furniture down the magma chute.
- Crimes
Births, immigrations, and deaths would be nice as well, but they're much more tedious to track by hand.
I like Ravaught's idea about linking it to nobles. Maybe it could work like the bookkeeper stats do - the player picks a detail level through the nobles menu, which determines how much time the little buggers have to spend updating the records and how much data is thrown at the player every year. Low detail would just be a diachronic version of the stuff on the status screen, highest would be the sort of crap only DF players would possibly care about.
After a few updates I'm sure this will turn into the world's best data porn. "Urist McRambo has severed three Third toe, left foot since joining The Bloody Sock in 783." "Urist McTyson has been punched in the head 352 times since immigrating to the fortress in 103." "13 dwarves have been killed by -copper bolt- this year." "Still #3 brewed 500 liters of dwarven wine last year." "1066 fluffy wumblers have died since the founding of Beardmurdered."