Okay, I've included the pitchers I've been using the whole time, plus a couple others (Jack Morris, Bert Blyleven, Nolan Ryan):
First, sorted by the number of times they led their league in ERA+:

This just shows the sheer dominance of Clemens, Johnson, and Pedro. Most pitchers had one or no first place finishes. Mussina, Smoltz, and Schilling, three of the guys talked about most in this thread, never led their league in ERA+.
Second, sorted by the number of times they finished in the top 5 of their league IN ERA+;

Still shows the dominance of Clemens, Pedro, and Johnson, but more guys show up with a bunch of years now. Mussina and Blyleven are tied with Martinez and Gibson, but that obviously doesn't show that Martinez's top 5 finishes included 5 first place finishes, and that the approximate level of the top 5 finishes of Martinez and Gibson were much higher than those of Mussina's and Blyleven's. Even so, it does show that Mussina and Blyleven spent a good chunk of time near the top of their league.
Lastly, sorted by the number of times in the top 10 of their league in ERA+:

Interesting that Blyleven and Mussina were only bested by Seaver and Clemens. Again, this doesn't illustrate that Mussina and Blyleven never had huge gigantic peaks like a number of the other pitchers. It does illustrate, though, that these guys managed to stay close to the top of their league much longer than most other pitchers do. Hunter and Morris are clearly the "odd men out", and they also happen to be the only two pitchers on this list that I don't think belong in the Hall at all.