With your typical MMORPG, players can usually farm the world for raw materials essentially forever. MonstersMonsters/mineral veins/etc are usually on some sort of respawn timer so, so other than time, there really isn't a good way to limit the amount of new currency entering the system.
So thatThat really only leaves money sinks to try to take money out of the system. WhatWhat are some strategies to prevent inflation of the in-game currency?