suggestions for triggers of my database project

Hi,
I am doing a project for my summer database course using oracle. It is about a bank system. the table i have on my sql are customer, holder, account, card type, card, transactions, exchange rate. the required triggers i was asked to do where lov's autonumber. i was asked to think about some which are innovative ones. can anyone suggest any innovative trigger. i dont need the syntax. i just need to know what the trigger does in that situation. thanks 4 ur time