I concur that the Jeannie Robertson book is really good, and I can't wait to see the Martin Carthy one. One that's a bit more obscure is Never Without a Song, by Katharine D. Newman (1995). It's about the life of a working woman between the years 1865 and 1952 in Pennsylvania and New Jersey, and the importance of folksong in her world. It's about 100 pages of biography followed by 175 pages of song texts, tunes and notes on repertoire. Fascinating if you're interested in traditional singing in that place and that period.

A similar one, but much much heavier on the songs and lighter on the bio, is Edith Fowke's book on LaRena Clark, A Family Heritage (1994).