I do have Standing in the Shadows; Jamerson is up there for me in the heroes department, but haven't really tackled his style.
I know people have been recommending his recordings already, but if you want to get into sightreading with some fun stuff (assuming that you know the basics?) I highly recommend the book Standing in the Shadows of Motown, with dozens of notated James Jamerson basslines, and a Cd that is great fun to play along with. For some simpler reading stuff (I think I sort of started with these), try some of the Bach cello suites, assuming you're at least somewhat into classical music and wouldn't kill yourself playing them. I used the Josquin des Prez book (not the composer, the writer), and taped over the tablature, which really helped.