Beyond The Boxscore has a good article on Davis called Willie Davis, underrated ballplayer (1940-2010). He currently ranks 124th in WAR all-time with 57.1 at Sean Smith's site.
Many are mentioning how fast he was. I have a theory that fast players (or at least guys who run the bases well), have a high triple-to-double ratio. Some fast players might not hit that many triples because they just don't hit the ball hard enough or far enough. And some guys who hits lots of triples might not be that fast. They might just hit the ball well.
But if a player has alot of triples relative to doubles, then it means that he is able to turn long hits into triples. You have to be fast to do that. If you get thrown out trying to stretch a double into a triple, you get credit for a double.
A few years ago, I did a study where I found the players with the best triple-to-double ratios of all-time (it actually involved standard deviations). It was The Fastest Players Since 1900 According to the Triple-to-Double Ratio. Davis ranked 65th out of 856 players. That puts him in the top 8%. His career ratio .349 (138/395) was almost double what it was in the NL from 1962-1976 (the bulk of his career) at .189.
But he may bave been hurt by his home parks in this measure (mostly Dodger Stadium). His career ratio at home was .267 (48/180). On the road, it was .419 (90/215). My guess is that a fair home park would bump him up in the rankings quite a bit. See The Batting Splits for Willie Davis at Retrosheet. His 138 triples is 66th all-time. He finished in the top ten 10 times, the top five 6 times and led the league twice.
Beyond the Boxscore had a good article about Garciaparra and how he had a great peak value caled How Good Was Nomah's Prime?. It looks like it was very good.
Garciaparra's best two years in offensive winning percentage were .767 (2000) and .743 (1999). There have only been 52 seasons by shortstops with a .700+ OWP (400+ PAs qualifier). Both of Garciaparra's seasons are in the top 25. Honus Wagner has the top 2 and 7 of the top 8. Data from the Lee Sinins Complete Baseball Encyclopedia.