As far as I've been told and remember...
Apparently all of my mother's side emigrated together from Austria-Hungary 3-4 generations back. Ethnically that doesn't lead you very far, but based on surname and religion they were probably Croats, Czechs, or Slovenes, leaning toward the latter two, I imagine.
My father's side is pretty much mixed, based on the prevalent populations of where they're from, probably some mix of British (Scottish/Irish more than English I'd imagine), German, Slavic and Italian. Pretty standard European-American mix.