At the [wiki entrance for Arya][1] the following list is given:

Dead

*   King Joffrey. Posioned by Olenna Tyrell.
*   Ser Amory. Eaten by Vargo Hoat's bear.
*   The Tickler. Arya killed him herself at the Crossroads Inn.
*   Polliver. Killed by The Hound at the Crossroads Inn.
*   Ser Gregor. Died in extreme pain due to the thickened manticore venom that coated Prince Oberyn's spear.
*   Raff the Sweetling. Killed by Arya under her guise of "Mercy" at the Gate, a mummers playhall in Braavos. 

Alive

*   Ilyn Payne
*   Meryn Trant
*   Queen Cersei
*   Dunsen 

Removed

*   The Hound 

Source: http://awoiaf.westeros.org/index.php/Arya_Stark#Arya_and_Death

  [1]: http://awoiaf.westeros.org/index.php/Arya_Stark#Arya_and_Death