The Hardball Times has an article up right now, ranking the best pitchers of all-time based on "Win Shares Above Bench."
You can see the definition of "Win Shares Above Bench" here, but in a nutshell, it seeks to measure how much better a player did over what an average bench player would have done, so if a player hangs around for 10 seasons and is a scrub, those 10 seasons of additional Win Shares don't artificially boost his performance level.
Anyway, something you might want to check out...of particular interest is that 2 of the top 10 pitchers on the list are active (well, 1 is active, and 1 can't make up his mind about whether he is retiring or not), and Gaylord Perry and Bert Blyleven are both ranked ahead of Nolan Ryan (who comes in at #30).