At the moment there are currently no plans for a Pirates of the Caribbean 5, although we will probably learn more about a potential sequel to Pirates of the Caribbean: On Stranger Tides once it is released May 2011 as Disney and director Rob Marshall may decide to leave a few doors open for future films.
On Stranger Tides will introduce a number of new characters such as Ian McShane and Blackbeard, Penelope Cruz as his daughter Angelica, Stephen Graham as Scram, Astrid Berges-Frisbey as mermaid Syrena and Sam Claflin as Philip, a youthful missionary. These characters could return for Pirates of the Caribbean 5 depending on where their storylines take them in the 4th film.
As for Johnny Depp as Captain Jack Sparrow, there is a possibility he could return if he still feels excited about playing the character (and if Disney pays him well). Director Rob Marshall may want another adventure on the high seas too, as On Stranger Tides will be his first Pirates of the Caribbean film.