According to Baseball-Reference.com, here are the 12 best seasons in the majors since 1901 by players in their last major-league season; I've added a brief note after each player to explain why it was his last season ...
1. Joe Jackson (7.3 Wins Above Replacement) - Banned
2. Happy Felsch (5.2) - Banned
3. Roberto Clemente (4.7) - Died
4. Jackie Robinson (4.3) - Traded / Retired
5. Roy Cullenbine (4.2) - Released
6. Chick Stahl (3.9) - Suicide
7. Will Clark (3.8) - Retired
8. Ray Chapman (3.7)- Killed
9. Barry Bonds (3.2) - Embarrassing
10. Hank Greenberg (3.2) - Retired
11. Buck Weaver (3.2) - Banned
12. Jim Doyle (3.2) - Died
Of those dozen players, only three simply quit: Jackie Robinson, Will Clark, and Hank Greenberg.
Robinson quit because he'd been traded from the Brooklyn Dodgers to the New York Giants, and simply didn't want to play for a new team. Well, there was that; also, Robinson had already decided to retire even before the trade, had accepted a significant amount of money to tell the story of his retirement in a magazine, and didn't want to give the money back.
Greenberg actually quit a year later than planned; he agreed to play one season with the Pirates only after they agreed to a whole set of demands, including no train travel, his own hotel suites, and a sterling $100,000 guaranteed income plus attendance bonuses. The Pirates were terrible that season, but Greenberg played pretty well despite a couple of nagging injuries. After the season, he got another offer to come back and play but declined, and instead went into management as an executive with, and minority owner of, the Cleveland Indians.
I don't have the slightest idea why Will Clark quit.
Roy Cullenbine was simply unappreciated, in his time. In 1947, Cullenbine batted just .224 in 142 games. He finished fourth in the American League with 24 home runs, and third in the league with a .401 on-base percentage. The Tigers released him. He went to spring training with the Phillies in 1948, but they released him too. And he didn't continue his career in the minors, which veterans players often did in those days. I've always figured there was more to this story, but I've not yet seen it.
Cullenbine's one of the nine players on that list who didn't really have a choice. He and Bonds were both unwanted, while three Black Sox were banned from Organized Baseball and four were dead: Stahl drank carbolic acid, Doyle died after suffering a burst appendix, Chapman died after getting beaned, and Clemente was killed in a plane crash, while on a relief mission to earthquake-stricken Nicaragua.
Chipper Jones is on pace to finish the season with 4.2 Wins Above Replacement, which would give him one of the five or six best last seasons in major-league history, and place him among the very best players to voluntarily leave the majors. He's played in only 62 of the Braves' 100 games this season, but still ranks among the better third basemen in the National League; rate-wise, he's been among the league's three best-hitting third basemen. He's got a 136 OPS+, just a few points lower than his career mark (141).
The problem is, it would be difficult for Chipper to come back for one more season, because he's told everyone he's not coming back, and so he's been gathering trophies and commemorative third bases and the like. Hey, maybe he did this on purpose. Maybe he thought he wanted to retire after the season, but was afraid that if he didn't go through the whole farewell tour and wound up having a good year, he wouldn't be able to resist coming back for another go-round in 2013.
I'm a baseball fan. And I will say, right now, that I won't hold it against Chipper if he wants to come back. I won't hold it against him if keeps all the swag, and I won't hold it against him if he comes back next season and doesn't play nearly as well as he's played this season. I just want him to keep playing for as long as he's still good, and he sure looks like he can be good for yet one more season, even after turning 41.