Financial services. My favourite would be a method where I can pay my bills using bitcoins.
Example: I have a bill for 499 EUR, the bank account number, due date and reference number. I supply that information to some company, and pay the company 499/mtgox_spotprice*1.01 bitcoins. The company pays my bill on due date.
The advantages? I could pay my rent and visa bill with bitcoins - essentially that would mean that I could have a "bitcoin credit card".
I don't know for what price someone would be able to offer this kind of service, but it would be certainly very useful for people who want to hold their money as bitcoins.
I wonder if Bit-Pay could add a feature like this...
1) You have a bill to pay
2) Bit-pay implements a "bill pay" option where you can enter in the address of your bill payment
3) You send Bitcoins to Bit-Pay, Bit-Pay converts Bitcoins to the currency of your choice
4) Bit-pay sends out your bill payment in the form of a check
5) Any residual funds are either refunded to you (minus a small transaction fee), or they are stored and carried over to the next month