Another graffiti artist that became quite famous is Jean Michel Basquait.
There is a good movie called Basquait out that tells quite a lot about him.
I don't know the age you are teaching. You should definitely preview it
before showing it to class. (Includes drugs as he was addicted to heroin.)
Keith Haring was a New York graffiti artist, as was Basquait.
Another that comes to mind is Kenny Sharf, but i'm not sure if he is
graffiti or mural artist.