If the dent is purely cosmetic you are better off living with it...since accidental damage is not covered under warranty it will cost several hundred dollars to replace the case. Taking a dent out of a machined aluminum piece is almost impossible.
You may be able to find a repair shop that can do the work but if the MBP is still under warranty doing so will probably void the warrranty.
you can use one of these shells for your Macbook to hide the dent if it bothers you.
getting it fixed will cost a few $$$ for something that's just what Ralph Landry states.