Watch the Appendix online guitar lesson by David Hamburger from New School Fingerstyle
The steady thumb groove is widely considered to be the province of Texas bluesmen, in particular Mance Lipscomb and Lightnin' Hopkins. This approach is also sometimes referred to as the "dead-thumb" style. I got most of my ideas about playing walking bass on the guitar from the music of John Renbourn and Joe Pass, in particular Renbourn's tune "Snap a Little Owl" and Pass' work with Ella Fitzgerald on their record "Fitzgerald and Pass Again" (Pablo).
Reference Source: Joe Pass (http://en.wikipedia.org/wiki/Joe_Pass)