Just short of 20 years ago, Reggie Jackson hit the 563rd home run of his 21-year career. That was the last home run he hit, and he finished that season as one of only 14 players with at least 500 career homers. From 1920 -- roughly speaking, when players actually began to hit home runs -- through 1987, there were only 14 players with 500 homers.
Frank Thomas just hit his 500th homer, which means that in the 20 years since Jackson took his last swing, membership in the 500 Club has increased by 50 percent, from 14 players to 21. And by the end of the 2008 season, it's likely five more members will have joined. Alex Rodriguez (492) isn't far behind Thomas. Jim Thome (482) and Manny Ramirez (481) are locks to reach 500, and Gary Sheffield (472), given even just reasonable health, will clear 500 next summer.
Jackson is in the Hall of Fame, and so are the 13 players before him who reached 500 homers. More than nine years passed before another player joined Jackson; in 1996, Eddie Murray hit his 500th, and he has a plaque in Cooperstown, too. That made the 500 Club 15-for-15 in the Hall of Fame.