If it's all about length, then put the Toy Cannon on the list. He'd belong there just as much as Allen.
But if the question is "Is there a player who, in his prime, would cause you to drop everything just to watch him take an at bat?" - Gotta say that my preferences will lean towards the guys who were not only sluggers, but great all around hitters.
Pujols, Howard, Mantle, Mays, Griffey, Aaron: these guys were great all around hitters.
Reggie, Strawberry, McGuire, Allen: these guys were all one dimensional sluggers for the most part.
Bonds? Lord knows what he would have been without the chemical assistance.
Forrest Snow - Was pitching well the last half of the season.
Now suspended for 50 games. Come on, Forrest. Just because it's legal in Washington...
2013 AAA/AA: 5-5, 2.96 ERA, 84 K, 28 BB, 1.085 WHIP
2012 AAA/AA: 5-9, 6.35 ERA, 99K, 67 BB, 1.674 WHIP
Gone But Not Forgotten (former adopt-a-players):
Eric Thames - Released to make room on the 40-man for 1.5 games from Gutierrez. Hitting .295/.382/.479/.861 in AAA at the time.
Matt Mangini - Signed a minor league contract with the Reds in the off season, but appears to have been handed his walking papers.
Mike Morse - HEY! Look who's gone again!!!!!
Jamal Strong - Let go after 2005. Played in the Yankees, Cubs and Braves systems. Now a regional scout for the Cards.