English Folk Song From The Southern Appalachians. Collected by Cecil J. Sharp and Maud Karpeles. Oxford university press.
Ozark Folksongs (four volumes!!!). Collected & edited by Vance Randolph. University of Missouri press.
Songs of American Sailormen. By Joanna Colcord. W.W. Norton & Company. Copyright 1938, might be hard to find.
And for Irish songs...
Sam Henry's Songs Of the People. Edited by Gale Huntington, revised by Lani Herrmann. University of Georgia Press.
These are excellent collections, right up there with Sandburg & Lomax.