I am always shocked that Ron Artest is never in this conversation. He is VERY physical and borderline malicious on a game to game basis.
As for the other players mentioned, I think Bowen is definitely a physical player but I don't consider him as dirty as Fortson. DF seems to try to hurt players. And no, I don't buy that Bowen is trying to hurt people, he just plays sneaky, cheap defense. Bowen reminds me a lot of the way Stockton used to play D. He would regularly step into players in the air and he was normally called "gritty" and "hard-nosed", not dirty.
I don't think Kobe's arm flailing is dirty. Just a cheap way to pick up a foul.
Stephen Jackson is not dirty, just dumb....
And to be honest, Raja is definitely physical to the point of being borderline cheap. He plays hard D that from time to time goes over the line (anyone remember the clothesline???).
I miss the days where what Raja does was the norm and if a player like Bowen stepped over the line (which he has done more than once), he would get a nice retributive shot from one of the bruisers on the opposing team.
Just my two cents....