Ok, this is my suggestion: Guild Lottery. Its organizing is pretty easy and its a good way to gain some gold to guild bank. The system would function so that once a month there is a lottery with a 5k price. We would need someone reliable to manage lottery tickets. One ticket would cost 150g and the ticket would be sent to "LTM" (Lottery Ticket Manager). To win the 5k price the participants should guess the right number between 1 and 1000 for the month which is set by the LTM each month. As tickets we would use ingame mail, which would be in following format:
1. Subject: Lottey Ticket
2. Your Name
3. Your lucky number
4. Add 150g participation payment
At this poitn your ticket is ready and can be sent to current LTM.
Example:
Once the ticket is send and recived by the LTM he deposits the 150g in the guild bank. At the lottery day the LTM checks if someone has guessed the number he has picked for that months lottery. If so, the LTM withdraws 5k gold from guild bank and sends it to that player who has won. If multiple players has got the right number, the price is equally divided between the players who has the winning number. If no-one gets the right number, the guild will get richer
Important note: The LTM MUST SAVE each lottery ticket players send. Either in mailbox, bags or bank (i suggest mailbox).
EDIT: LTM isnt allowed to participate, suprise suprise xD