I play on a server which has no market plugin, and with the incoming 1.5 update, I decided to make a shop system. It lets any player trade one diamond for a certain amount of resources; This way you can make a real, functionnal market place, without the need of any plugin. I didn't tested but the system is quite bug-free and should work even with lag
Here is the video with a demonstration and a tutorial:
Please feel free to comment if you have any suggestions or questions!