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.
Gone But Not Forgotten (former adopt-a-players):
Forrest Snow - Signed a minor league deal with the Brewers in the off-season. Good luck Forrest!
Alex Jackson - Traded to Atlanta after underwhelming in three years of pro ball.
Eric Thames - Brought back to MLB by the Brewers after hitting .347/.448/.714/1.162 in Korea the past few years.
Matt Mangini - Out of baseball. Now sells cigars and offers baseball training/evaluation services.
Mike Morse - Now 35 and competing for a job with the SF Giants.
Jamal Strong - Let go after 2005. Played in the Yankees, Cubs and Braves systems. Now a national scout for the Cards.