My connection is not too good, and it fades in and out. On a good day, when I want to make gold fast, I go to the daemon room in Fire Dungeon, invis myself and keep two EVs spinning at a time; they take down a daemon in ~7 seconds, and the daemons respawn every thirty seconds or so. It's confined, but if a daemon targets me, I can head for the teleporter in the middle of the room and make a quick escape. (Do not move once you're on the teleporter. Don't try to run through the flames; they always rubber-band me. Use teleport instead, and make sure you have a rune back upstairs.) You probably already know this, but daemons give about 600-700gp each. Alternately, there's Wind, if you have magery.
On a bad day, when I'm laggy, I fight crystal elementals. There's a pretty much constant spawn within a few screens of the little ruin in the Crystal Fens, although you have to run around. Each elemental gives ~400gp, and also four gems; if you collect the gems, you make double the money pretty much every time. Crystals are low-fame, though, so there's not as much of a double reward as there is with daemons. They're just better for laggy days.
I'm not much of a fighter, though, so I don't tackle the big stuff. There'd be harder things that give more gold; this is just what I do when I find myself low on funds.
