Jleg says none, and while this is technically true, I think some other things you may consider 'hidden costs' should be mentioned.
While techncially there are no other charges that you're forced to pay, there are plenty of things that add to your overall cost of the trip that you may not think about if you've never cruised before and haven't done a lot of research.
1- While food is included, you must pay for alcohol and soda.
2- Of course you must pay for your excursions on shore.
3- Movies in room have a charge
4- Basic toilteries are supplied, but you may need to buy some
5- Photos the crew takes of you are expensive, if you choose to buy
6- Internet has a charge
Most of these are probably obvious, but I thought I would elaborate on the previous answer given.