J.M. Flagg
John Held
Charles Dana Gibson
Antonio Vargas
He also did some nifty, deliberately antique woodcuts, disguised social commentary, sort of like Dicky Doyle's ye customes of ye Englishe in 1842.
Other forgotten masters:
Harvey Dunn, in war and peace
A.B. Frost
Rockwell Kent (even if he WAS a Commie).