Over at Futility Infielder they have an interesting Hall of Fame analysis for baseball relievers. FI revamps a stat introduced by Rich Rifkin called the Hoyt Scale. It is interesting to see pitchers from different eras compared in one scale.
I feel that I cannot accurately comment on the Hoyt Scale until I complete my history of relievers. I plan on having my own means of comparing relievers over time at the end of it. Like most of American culture, I am currently stuck in the '70s. It is the decade in which the greatest amount of change occurred in relief pitching. The experimentation of '60s led to new approaches. The sticking point for me is the development of the 5-man rotation and its effects on relief pitching. I should have something out soon though.