Lefty Grove. He was a great pitcher, who is almost always overlooked because he pitched during the first live ball era. His numbers aren't as pretty as guys who pitched just 15 years before but that is no reason to down play his greatness.
Hubbell was a very good pitcher as well. he compiled a streak of 46 1/3 scoreless innings in 1933 and won 16 straight games in 1936 (and a record 24 over two seasons). And lets not forget the 1934 All-Star Game when he fanned Babe Ruth, Lou Gehrig, Jimmie Foxx, Al Simmons and Joe Cronin - in succession
Lets see RJ strike out 5 hall of famers in a row.