If I had to recommend one bass player to listen to in order to improve your own bass playing it would be James Jamerson. He had the lot: groove, taste, soul, flair, tone, and more.
This lesson breaks down a few simple ideas you can use to make up Motown bass lines. As with many things you'll learn with bass, much of what you find out can be transferred to other styles.
Scroll down for the PDF and backing track.
Motown Backing Track
The following PDF lays out some of the shapes used in the video. To delve deeper into harmony and shapes, you might find the following lessons helpful:
I don't know if you caught it, but the backing track and lesson is based around some of the chords from one of the greatest bass lines of all time; Jamerson's masterpiece on What's Going On. A stunning piece of music!