Money

Go out and hunt you lazy shits

Hunting
Any level ''Swamp trolls drop medicine pouches at a pretty uncommon rate. These items, depending on the server, can be sold for a modest amount. If you gamble, however, there is a chance that they can turn into significantly more gold. Great for low levels, as they drop plenty of food and spears for paladins.''
 * Swamp Trolls

Quests at notable milestones
20 DQ

30 Paradox

To Appease the Mighty (pre-djinn)

35 Crusader Helmet

40

Sorc 33+ Prem
Go hunt Carniphilas. Carrot on a stick is worth a pretty sum, you'll often turn a profit.

Dailies
Aside from just hunting, there's items and quest you can collect/do on a daily basis to earn some dosh.

''Lucky Loop is a daily quest you can pick up after finishing Rottin Wood and the Married Men quest. It has a chance of rewarding a hunting horn, which is worth a hefty sum of gold.''
 * Lucky Loop

''Certain crates are usable and have a chance of rewarding you with various items(most notably: the dwarven rings, potions and brown shrooms). See here for locations.''
 * Crates

''While not the most expensive item, producing them in large quantities is relatively easy. See here for information on how to acquire them.''
 * Sugar Oats

''Sometimes, the game just throws money at you. See here for a list of items that respawn after every server save("ss") or floor reset.''
 * Daily Respawning Items