Reds:
Roger Salkeld (41) -The third overall pick in the draft by Seattle, he hurt his arm and never achieved the greatness predicted for him. A Red in 1996.
Ted Abernathy -The first pitcher to record 30 saves in a season. With the Reds in 1967 he threw 100+ innings with a 1.27 ERA. Threw underhand and was indescribably fun to watch.
Cookie Rojas (73) -Came up in the Reds system as a second baseman, but by the time he was ready for the bigs he was blocked by Billy Martin, Johnny Temple and Don Blasingame. Eventually carved out a career as a 2b-utility guy for several clubs, most notably the Royals. Currently does Spanish-language TV for the Marlins.
Others:
Wilver Stargell -Better known as "Willie", but he preferred Wilver. No one hit the ball farther than "Pops". Don Sutton said, "He doesn't just homer off of you, he takes away your dignity".
Pete Gray -Famous one-armed outfielder. He was a legitimate player; he was the Southern League MVP in 1944. When he got to the bigs, however, pitchers discovered that with only one wrist on the bat he couldn't adjust to breaking balls, and that was it for his career.
Lefty Grove -For my money, the best left-handed pitcher of all time.