First under appreciated player that pops into your head

[iwantitiwinit]

Albert Belle

[michael3322]

A lot of great responses here. I'd add 2:

Allie Reynolds

"Reynolds got his start in the majors as a solid pitcher for the Indians in the 1940s. However, once he got to the Yankees in 1947 his career took off. During his eight seasons in pinstripes, he went 131-60 with a 3.30 ERA. Reynolds helped the Yankees to six World Series titles, racking up a 7-2 record with a 2.79 ERA over 15 World Series games.

Reynolds made five All-Star games and had two top-three MVP finishes. Reynolds got a late start to his MLB career and pitched in only 12 full seasons. As a result, his final career numbers don't match up with the great pitchers of his generation. But when he was at his best, Reynolds could pitch with anybody."

and...

Lefty O'Doul

"O'Doul is in the Japanese Baseball Hall of Fame and is credited with helping to popularize the sport in Japan in the 1930s. Before that, O'Doul had some great seasons as a left fielder after being converted from a pitcher at the age of 31. O'Doul had just seven full seasons as an offensive player, but he had two top-three finishes in MVP voting.

O'Doul had one of the greatest offensive seasons in major league history in 1929 when he set a National League record with 254 hits. He batted .398 that season and led the league with a .465 on-base percentage. O'Doul finished his career with a .349 batting average, still the fourth-best in major league history.

His best season on the Hall of Fame ballot came in 1960, when he received 45 Hall of Fame votes, a total higher than 27 future Hall of Famers. He had more votes than players like Ralph Kiner, Chuck Klein, Lefty Grove and Lloyd Waner."

[alaskapaul3]

First name that popped into my head was Aramis Ramirez. Completely consistant. Not a HOF , but should have at least stuck around on the ballot.