I've listed first and second place for each 3-year period.
2009-2011: Albert Pujols 21.7 Evan Longoria 20.5 2008-2010: Albert Pujols 25.9 Joe Mauer 22.5 2007-2009: Albert Pujols 27.1 Joe Mauer 21.2 2006-2008: Albert Pujols 26.2 Joe Mauer 20.3 2005-2007: Albert Pujols 24.8 Alex Rodriguez 22.5 2004-2006: Albert Pujols 25.9 Alex Rodriguez 18.8 2003-2005: Albert Pujols 28.5 Barry Bonds 23.1 2002-2004: Barry Bonds 34.9 Albert Pujols 26.1 2001-2003: Barry Bonds 35 Alex Rodriguez 23.9 2000-2002: Barry Bonds 33.4 Alex Rodriguez 27.2 1999-2001: Barry Bonds 25.2 Jason Giambi 25 1998-2000: Alex Rodriguez 23.6 Andruw Jones 22.1 1997-1999: Jeff Bagwell 22.5 Barry Bonds 22.1 1996-1998: Barry Bonds 28.9 Ken Griffey 25.2 1995-1997: Barry Bonds 26.9 Ken Griffey 22.6 1994-1996: Barry Bonds 24.5 Jeff Bagwell 22.6 1993-1995: Barry Bonds 24.3 Jeff Bagwell 19.4 1992-1994: Barry Bonds 27 Kenny Lofton 20.8 1991-1993: Barry Bonds 28.9 Frank Thomas 21.7 1990-1992: Barry Bonds 28 Cal Ripken 20.9 1989-1991: Barry Bonds 25.7 Cal Ripken 24 1988-1990: R Henderson 25 Barry Bonds 23.6 1987-1989: Wade Boggs 26 Will Clark 21.1 1986-1988: Wade Boggs 26.4 Alan Trammell 20.3 1985-1987: Wade Boggs 26.2 R Henderson 20.4 1984-1986: Wade Boggs 22.9 R Henderson 21.9 1983-1985: R Henderson 23.7 Cal Ripken 23.6 1982-1984: Robin Yount 25.2 Cal Ripken 22 1981-1983: Robin Yount 24.2 Mike Schmidt 23.2 1980-1982: Mike Schmidt 24.6 Robin Yount 23.4 1979-1981: Mike Schmidt 24.1 George Brett 20.9 1978-1980: George Brett 23.4 Mike Schmidt 22.7 1977-1979: Mike Schmidt 23.2 George Brett 21.4 1976-1978: Mike Schmidt 24.3 Rod Carew 22.6 1975-1977: Joe Morgan 28.2 Rod Carew 26.3 1974-1976: Joe Morgan 31.1 Mike Schmidt 26 1973-1975: Joe Morgan 31 Rod Carew 21.6 1972-1974: Joe Morgan 29 Johnny Bench 21.7 1971-1973: Joe Morgan 25.1 Willie Stargell 25.1 1970-1972: Bobby Murcer 19.4 Johnny Bench / Roy White 19.3 1969-1971: Sal Bando 21.4 Hank Aaron 19.8 1968-1970: C Yastrzemski 23.8 Willie McCovey 22.4 1967-1969: C Yastrzemski 26.9 R Clemente 22.7 1966-1968: C Yastrzemski 26.9 Ron Santo 24.1 1965-1967: Ron Santo 26.1 Willie Mays 24 1964-1966: Willie Mays 29.9 Ron Santo 23.8 1963-1965: Willie Mays 31.4 Hank Aaron 24.1 1962-1964: Willie Mays 31 Hank Aaron 25.9 1961-1963: Willie Mays 30.2 Hank Aaron 28 1960-1962: Willie Mays 29.7 Hank Aaron 26.4 1959-1961: Willie Mays 26.6 Hank Aaron 26.4 1958-1960: Ernie Banks 27.9 Willie Mays 27.6 1957-1959: Mickey Mantle 28.4 Ernie Banks 26.4 1956-1958: Mickey Mantle 35.2 Willie Mays 25.7 1955-1957: Mickey Mantle 34.9 Willie Mays 24.6 1954-1956: Mickey Mantle 30.2 Willie Mays 26.3 1953-1955: Duke Snider 26.1 Eddie Mathews 25 1952-1954: Stan Musial 22.9 Duke Snider 22 1951-1953: Jackie Robinson 25.8 Stan Musial 24 1950-1952: Jackie Robinson 26 Stan Musial 22.7 1949-1951: Jackie Robinson 27.6 Stan Musial 23.7 1948-1950: Stan Musial 26.5 Jackie Robinson 23.3 1947-1949: Ted Williams 28.7 Stan Musial 25 1946-1948: Ted Williams 31 Stan Musial 26.1 1945-1947: Ted Williams 22.1 Whitey Kurowski 16.2 1944-1946: Stan Musial 18.9 S Stirnweiss 18 1943-1945: Augie Galan 18.7 Stan Musial 18 1942-1944: Stan Musial 23.8 Bill Nicholson 18.8 1941-1943: Ted Williams 22.3 Charlie Keller 20.3 1940-1942: Ted Williams 28.3 Joe DiMaggio 23.5 1939-1941: Joe DiMaggio 25.6 Ted Williams 24.1 1938-1940: Joe DiMaggio 22 Arky Vaughan 20.6 1937-1939: Joe DiMaggio 23.7 Mel Ott 20.7 1936-1938: Mel Ott 22.7 Lou Gehrig 22.6 1935-1937: Lou Gehrig 27.4 C Gehringer 23.9 1934-1936: Lou Gehrig 29.7 C Gehringer 25.8 1933-1935: Lou Gehrig 27.8 Jimmie Foxx 25.8 1932-1934: Jimmie Foxx 28.5 Lou Gehrig 27.2 1931-1933: Babe Ruth 27.3 Lou Gehrig 26.2 1930-1932: Babe Ruth 31.1 Lou Gehrig 28.3 1929-1931: Babe Ruth 30.3 Lou Gehrig 27.3 1928-1930: Babe Ruth 29.9 Lou Gehrig 27.7 1927-1929: Babe Ruth 32 Rogers Hornsby 30.3 1926-1928: Babe Ruth 35.8 Lou Gehrig 29.1 1925-1927: Babe Ruth 27.7 Rogers Hornsby 24.7 1924-1926: Rogers Hornsby 27.4 Babe Ruth 26.8 1923-1925: Rogers Hornsby 29.5 Babe Ruth 29.5 1922-1924: Babe Ruth 30.2 Rogers Hornsby 30.2 1921-1923: Babe Ruth 34.9 Rogers Hornsby 28.9 1920-1922: Babe Ruth 33.1 Rogers Hornsby 31.8 1919-1921: Babe Ruth 37.5 Rogers Hornsby 27.6 1918-1920: Babe Ruth 29.7 George Sisler 21.1 1917-1919: Ty Cobb 25.3 Rogers Hornsby 20.5 1916-1918: Ty Cobb 27.7 Tris Speaker 21.5 1915-1917: Ty Cobb 31.6 Tris Speaker 24.5 1914-1916: Eddie Collins 27.6 Tris Speaker 26.8 1913-1915: Eddie Collins 31.8 Tris Speaker 26 1912-1914: Eddie Collins 30.9 Tris Speaker 28.9 1911-1913: Ty Cobb 28.6 Eddie Collins / Joe Jackson 26.9 1910-1912: Ty Cobb 32.7 Eddie Collins 25.9 1909-1911: Ty Cobb 33 Eddie Collins 26.5 1908-1910: Ty Cobb 28.3 Honus Wagner 26.1 1907-1909: Honus Wagner 31 Ty Cobb 25.7 1906-1908: Honus Wagner 31.6 Nap Lajoie 22.8 1905-1907: Honus Wagner 30.6 George Stone 19.9 1904-1906: Honus Wagner 29.6 Nap Lajoie 22 1903-1905: Honus Wagner 27.5 Nap Lajoie 20.3 1902-1904: Honus Wagner 25 Nap Lajoie 22.9 1901-1903: Honus Wagner 23.9 Nap Lajoie 22.6 1900-1902: Honus Wagner 23.1 Nap Lajoie 19.4
Notes:
- Highest WAR over a 3-year period: Ruth (37.5, 1919-1921), Ruth (35.8, 1926-1928), Mantle (35.2, 1956-1958), Bonds (35.0, 2001-2003), Bonds (34.9, 2002-2004)
- Most times leading: Ruth 12, Bonds 12, Wagner 8, Pujols 7, Cobb 7, Mays 6, Morgan 5, Williams 5
- Lowest leading WAR total: Galas (18.7, 1943-1945, caused by World War II), Musial (18.9, 1944-1946), Bobby Murcer (19.4, 1970-1972), Sal Bando (21.4, 1969-1971), Albert Pujols (2009-2011)
- Just to reiterate the last bullet point, Pujols' leading total from 2009-2011 is the 5th lowest since 1901.
- Most second-place finishes: Lou Gehrig 7, Rogers Horsnby 7, Hank Aaron 6, Nap Lajoie 6, Stan Musial 6, Tris Speaker 5, Willie Mays 5, Cal Ripken 4, Alex Rodriguez 4
- Aaron, Lajoie, Speaker, and Ripken never finished first.
- Following are the winners who led second place by the highest percentage: Wagner (1905-1907, 54% more than second-place total), Bonds (2001-2003, 46%), Morgan (1937-1975, 44%), Mantle (1955-1957, 42%), Ruth (1918-1920, 41%)
- Following are periods when there was a tie between the first and second-place finishers: 1922-194 (Ruth, Horsnby), 1971-1973 (Morgan, Stargell), and 1923-1925 (Hornsby, Ruth)
- Some other names that might surprise you: the aforementioned Augie Galan, Sal Bando, Alan Trammell, Andruw Jones, Bill Nicholson, George Stone, Kenny Lofton, Roy White, Stuffy Stirnweiss, Whitey Kurowski, and Will Clark.