There's a lot to be learned from looking over PFR's leaderboards. For example, we can see that Thurman Thomas absolutely should have been a first ballot HOFer, and he should absolutely make it in this year. He led the league in yards from scrimmage FOUR STRAIGHT YEARS (89, 90, 91, 92). For three of those years he was a contemporary of Emmitt Smith, for all four years he was a contemporary of Barry Sanders (each led the league in yards from scrimmage twice). Everybody looks at rushing yards and rushing titles, but yards from scrimmage tells us a lot about what a player is doing for his team. And Thurman Thomas, by this standard, was the most productive RB in the league for four consecutive years.
I also find it interesting to look at the year-by-year leaders in passing yardage and passing TDs. The game changes and the numbers from one era may look average compared to the numbers of another era; that's why it can be more useful to look at the year-by-year leaders. With such a list you get a sense of who was the best for his particular time. This is useful in other sports, too: in basketball, the game has changed and numbers themselves are difficult to compare, but we still can see that only four players have led the league in scoring four or more times (Chamberlain, Gervin, Jordan, Iverson).
I was looking these over because I think Tom Brady's stats often get overlooked. His reputation as a "winner" and "clutch performer" and his playoff record get the attention, but Brady has led the league in passing yardage (2005) and passing TDs (2002). He's not merely a "winner"--he's a very good NFL quarterback.
So for my own curiosity, I looked through PFR's leaderboards to see which QBs have led the league in both categories (not in the same year, but at all), and I have a blog to post just such study. So here's the list of players who have, at some point in their careers, led the league in both passing yardage and passing TDs in a season, since 1960. An * signifies a tie and an "a" signifies AFL leader.
Tom Brady (yards 05, TDs 02)
Peyton Manning (yards 00 and 03, TDs 00*, 04, 06)
Daunte Culpepper (yards 04, TDs 00*)
Kurt Warner (yards 01, TDs 99 and 01)
Brett Favre (yards 95 and 98, TDs 95, 96, 97, 03)
Dan Marino (yards 84, 85, 86, 88, 92, TDs 84, 85, 86)
Warren Moon (yards 90 and 91, TDs 90)
Lynn Dickey (yards 83, TDs 83)
Dan Fouts (yards 79, 80, 81, 82, TDs 81 and 82*)
Fran Tarkenton (yards 78, TDs 75)
Roman Gabriel (yards 73, TDs 69 and 73)
John Hadl (yards 65a and 71, TDs 68a and 71)
John Brodie (yards 65, 68, and 70, TDs 65 and 70)
Daryl Lamonica (yards 69a, TDs 67a)
Sonny Jurgenson (yards 61,62, 66, 67, 69, TDs 61 and 67)
Babe Parilli (yards 64a, TDs 64a)
John Unitas (yards 60, TDs 60)
George Blanda (yards 61a and 63 a, TDs 61a)