Finish the A Night To Remember quest and give 10000 gold to the Argonian who will later randomly show up. He'll buy a nice island in Black Marsh with it, instead of getting drunk with the 750 gold you'd otherwise give him through persuasion (if you didn't kill him).
Stock it in a chest, to use in times of need. You never know, maybe Skyrim will eventually be struck by famine etc. due to all the warring going on (it's kinda weird how most of the civilians stay pretty well-fed during civil war ...).
Start donating to temples, shrines, even tombs, word walls, ... Just put some money in those treasure chests instead of looting them completely empty, as a 'passage fee'/donation. I always stick a flower, Nord mead and some money in there with my Nord character, as a respectful gift.
...
Apparently on the PC you can drop coins. I'm on the PS3, but I wish I could build a giant tower and drop my coins down it. Then I'd jump in Scrooge McDuck style.
I remember someone saying he's done that, but eventually his pc froze everytime he entered the cell where his coins were dropped. I don't believe he'd dropped so many coins either ...
i put stacks of 10.000 on beggars randomly, only to have them wear the same rags and do their usual stuff even though they got enough money for nice clothes and a small house
the AI is dumb
Nah, the AI is fine on that matter. You really believe a beggar would suddenly become rational and buy the stuff he needs? Those guys have spent that money on booze big time. Probably had a nice party among themselves, the likes of which Sanguine would've been very proud.