There are four left fielders that stick out in Major League history.

Barry Bonds, Stan Musial, Ted Williams and Rickey Henderson.

Musial actually played a few more games at first base than left field, and also several seasons in right field. However, that speaks to his versatility.

In terms of career wins above replacement, the four rank like this:

Bonds: 158.1 WAR
Musial: 123.4 WAR
Williams: 119.8 WAR
Henderson: 106.8 WAR