As an appendix to my RJ Centennial Collection recommendation, let me say further that digital magic has been done on the master tapes so somehow the guitar still has vibrancy and depth despite whatever processing has been utilized.....check it out!
Other good ones:
Slim Harpo - The Excello Singles Anthology (2003, Hippo/UNI, B000583-02)
Memphis Minnie - Hoodoo Lady (2008, Snapper Label, SBLUECD 050)
Elmore James - Blues After Hours (2005, Ace Records, CDCHM 1043)