I have made most of the gold I have through questing, farming, grinding karazhan (cloth and greens, enchanting materials, etc), even old instances. I sell what a lot of raw materials because on my server there are a lot of people that sell profession kits on a daily basis, so I usually have quick turnaround time on getting gold. I do this across 11 characters, so I can overcome the raid locks for the week, by doing at least one or two characters a day through Vanilla, BC, and Wrath content since it is really easy to plow through all of that stuff.
I do some of the Cata stuff, but I really never like that content, so I tend to skip it. I have also done every single quest in the game across at least 6/11 characters, every daily new and old mostly to grind rep. Making gold outside of the AH, takes time if your not willing to put forth the effort to farming it out then you are pretty limited in what you can make gold from in this game. Everyone here has made some very good suggestions, If you have blood DK, then you should be able to plow through a lot of content relatively fast even if its modestly geared.
I do all my farming in dps specs, I have little issue clear content even some of the MoP dungeon content and none of my characters have higher than a 530 ilvl.