The most popular spots are bosses in Wintertusk - Asrik, Erling, or Halfang are most used, but go with whatever you can beat fastest. If you don't have WT access, DS and CL have some ok boss drops. High level wizards may get gold as fast or faster by farming KR mobs, and that way you have a chance at jewel drops too.
Gardening is another good way to earn gold. Even stinkweed pays pretty well.
Hey, So, I never really had any problem with my gold, maybe because I don't use it that much but my gold does overflow a couple of times and I had to buy houses to use up my gold. I think you should just try to manage your gold better, try to prevent your gold from going lower than 100 000. Do more dungeons and sell all your useless gear cause it does give you a lot of gold. I normally go to the robe shop in shopping district to sell no auction gears. I usually farm a lot of places looking for jewels or better gear, but along that i find many useless gear i don't need. I used to always keep them, but then I realized how much gold I can get from selling them. So try farming mirror lake or malistaire or morganthe, you'll get a bunch of things to sell and you'll make a lot of gold in no time. Hope this helped!