Some more classics:

That's No Way to Get Along - Robert Wilkins
'Taint Nobody's Business - Frank Stokes
Fixing to Die - Bukka White
Come On In My Kitchen - Robert Johnson (along with the rest of the catalog)
Bullfrog Blues - William Harris (Check out David Bromberg's version)
Moon Going Down - Charlie Patton
Hard Time Killin Floor Blues - Skip James
Pigmeat - Leadbelly
Motherless Children - Blind Willie Johnson
Bad Luck Blues - Blind Lemon Jefferson
Fishing Blues - Henry Thomas
Back Water Blues - Bessie Smith
Make Me a Pallet on Your Floor - Mississippi John Hurt
Diddie Wah Ditty - Blind Blake
Hesitation Blues - Rev. Gary Davis
Good Old Wagon - Bessie Smith

And on...and on...and on.