For us in Europe, it's life +70, so authors who died in 1939 become public domain today.
From the site indicated by kwjones:
Heywood Broun
Ethel M Dell
Ford Madox Ford
Zane Grey
Kyōka Izumi
Okamoto Kido
Joseph Roth
S S van Dine
W B Yeats
All unknown by me, except Yeats.
Van Dine seems to have writtern some nice mistery novels though, which are available thanks to HarryT:
link for the mobipocket version