I was in Ballymena recently and the graffiti was slim pickings. The problem was that a lot of the car parks in town that used to have the best graffiti have gotten rid of it. Instead of doing a complete repaint of the walls what has happened is the council have just painted big grey squares where the graffiti used to be. This doesn't in any way serve to improve the look of the area instead it makes it look bland and uninteresting.
Anyways one place I found some was in the subway at the entrance of the Dunvale estate where I grew up.
This looks to be the result of the community programs that usually result in inoffensive crap like zoo animals being painted up. As luck would have it, whoever did it used a hip-hop theme with the faces of various hip-hop artists and the slogan "Northsiders" (because Dunvale is in the north of the town).
These are from the entrance of to the subway
And these are from inside it