Work at the different jobs on offer... Blacksmith, Lumberjack, Bartender, Slave Rescue, Slave Trader etc etc (you can check what jobs are available in the jobs tab of your quests menu). I recommend building up Bartender as much as possible as it is probably the easiest & makes more gold for your time spent working than any other job.
Go Treasure hunting and sell the items you collect from various locations, or go treasure looting and sell the items you steal from peoples houses etc.
You can beg NPC's for gold or probably the easiest way to make fast cash is just to ask a bunch of players around you on Live if they have a few coin to spare (most people are in the high millions and wont mind giving you some of their gold).
Different Clothes stores(there are 2 in Bowerstone Market), Traveling traders, Chests, Box of Secrets shop (if you have the Knothole Island DLC) and probably something else I cant think of, just have agood look around its part of the fun of the game (exploration).