Anon is great
CupofTeas list for those where we know the author is a great place to start
Songwriters who have multiple works written in my lifetime that I believe will live on "in the tradition:"
Woody Guthrie
Pete Seeger
Eric Bogle
Gordon Bok
Phil Ochs
Sidney Carter
Tom Paxton
Andy M. Stewart
Tommy Sands

Personally I also would add Chris Wood/Hugh Lupton and John Tams