This is based on what I did last week to look at the best seasons. It involves finding base stealings runs (using the linear weights values) divided by times reaching first base. Then I found how much bigger that was than the league average and ranked the players. I looked at all players who had 200+ SBs since 1920 since that is when the AL started keeping a constant, year-by-year, track of caught stealing (the NL began in 1951). So a few NLers were left out: Pee Wee Reese, Richie Ashburn, Billy Werber, Frankie Frisch and Kiki Cuyler. I did included Max Carey since the Lee Sinins Complete Baseball Encyclopedia shows his CS for 1913-25, although I don't know how accurate that is. So the two tables below show the top 50.
Update: Tom Hanrahan just published something similar in "By The Numbers" called The Greatest Base Thief.