Larry, if you're interested in the songster tradition (though as Jeff pointed out, songster is a term that was laid on the music by critics and liner note writers in the 1960s and 70s), these are worth checking out:
Before the Blues Vols. 1-3 (Yazoo)
There are some white country groups and some religious music included, but they provide a good overview of the recorded evolution of the blues from its early roots. Some great music in the best possible sound.