Using Baseball Reference's Play Index, I came up with a list of the best player seasons by players in their final year. This list comprises players in their last season, playing 100+ games, sorted by OPS+.

1. Ted Williams

Playing in 113 games, Williams hit .316 with 29 home runs, 72 RBIs, and 75 walks (adding up to a .451 OBP). Announcing his retirement before the end of the season, Williams hit a home run in his final career at bat.

2. "Shoeless" Joe Jackson

This is actually 1920, as it took a season for the Black Sox scandal to break. Offenses around the league exploded, Jackson himself hit .382 with power and plate discipline. Jackson hit 42 doubles, 20 triples, 12 home runs, 121 RBIs, and only 14 strikeouts. With three games remaining in the season, Jackson and company were suspended by MLB in the wake of the Black Sox indictments. He was later banned for life the following season.

3. Nick Johnson

Johnson suffered a horrific leg injury in September of 2006 and missed the entire 2007 campaign. Will he ever play again? If not, note his .428 OBP for the Nationals in 2006, playing in a tough hitters' park.

4. Will Clark

After quietly producing quality seasons in Texas, Clark moved to Baltimore and missed half of the 1999 season. Clark played well in 2000 with the Orioles, staying healthy and again producing quality. Meanwhile in St. Louis, Mark McGwire suffered nagging injuries. The Cards looked to Clark as a stopgap, and Clark exploded, hitting .345 down the stretch and leading St. Louis to a Central division championship. The Cardinals tried to re-sign Clark for a LF job, but Clark elected retirement instead.

Let me note here that Clark's season in 1989 was every bit as good as Jim Rice's 1978, in context. Clark was a flat out better player with a better career, but of course got no Hall of Fame support.

5. Happy Felsch

See Joe Jackson. Felsch hit .338, collected 69 extra base hits, drove in 115 runners and played center field. Hall of Fame material? Probably not. He had a similar OPS+ careerwise as players such as Cesar Cedeno, Ray Lankford, Cy Williams and Rick Monday.

6. Mickey Mantle

When Mickey Mantle hit .237 with 18 home runs and 54 RBIs, he looked done. The composite batting line for the American League in 1968 was .233/.302/.346. Mantle's .782 OPS that season actually ranked 9th in the American League.

7. Dave Nilsson

Nilsson had something of a fluke season, hitting .309 in 115 games as a catcher. Nilsson departed after the season to play for Australia in the 2000 olympics, and has generally been an Australian baseball mainstay since.

8. Steve Evans

The only player on the list I never heard of. Evans jumped to the Federal League and had two very good seasons there in 1914-15. When the league folded, Evans disappeared from the majors.

9. Brian Downing

.407 OBP for the Texas Rangers in 1992 as a DH in 107 games. Downing had not played a game in the field since 1987, so only his bat carried him.

10. Buzz Arlett

Arlett hit .318/.387/.538 in his only MLB season with the Phillies. Arlett was a star in the Pacific Coast League, back when that meant something. Arlett could have easily had a productive career in the Majors, but like many players of his day preferred to stay closer to home in California.