Dragon scales sell well. The trick is finding the shops that have coin to buy. You'll have to find those on your own though. Can't give away my secrets there.

Some people farm high gold yield chests, but I find that unfun so I'd rather just go without that much money.

You can also kill mobs with lots of money. Frost giants come to mind. It's not quick, but you can get some skill practice in or something.

Luckily my Santa Zulgh came true and when you "list" at a shopkeeper it tells you what type of items they will buy.