Hootenany: I'd definitely recommend Jim Longhi's book. Bound For Glory certainly deserves reading, but with a very large pinch of salt.

I don't think anyone has yet mentioned How Can I Keep From Singing, David King Dunaway's excellent biography of Pete Seeger.
Also, Peter D. Goldsmith's Making People's Music: Moe Asch and Folkways Records.

There's also Dave Arthur's biography of A.L. Lloyd which seems to have been in the pipeline forever. Does anyone know what's happened to it?