"White trash" is the only insult I know that's often used by people who pride themselves on being exquisitely politically correct. Here are two manifestations that might actually be useful to writers writing about working class white folks:
The White Trash Name Generator | Rum and Monkey
And, from Ted:
PS. My niece's name is Brandi, and she's a better human being than anyone who's amused by her name.
ETA: Poor whites in the USA