Economy ideas for a Bukkit server

[SparcleeLasagnia]

I was wondering if there were any plugins or ways to allow people to earn money without selling items. Since people are able to duplicate items, they can get tons of money from it. So I wanted a way for players to be able to make money without selling items.

I did see one that gives you money from killing mobs, but thats not exactly what I had in mind.

[Whovian]

Question, what will the money be useful for if not items?

(And I was about to suggest an economy plugin or industrial credits, but those are rubbish and sell-able.)

[SparcleeLasagnia]

I have the residence plugin that costs money to claim land, and a shop where you can buy stuff, not sell.