#1 - Steve Carlton to the Phillies
This one just dumbfounds me, even more so than the other deals on this list.
Future Hall of Famer, Steve Carlton, was coming off his age-26 season with St. Louis, whom he'd been a three-time All-Star with already and amassed a 77-62 record with a 3.10 ERA in 1265.1 innings. The Cardinals had a young ace on their hands, but the Cardinals refused to pay him the $65,000 salary he was asking for and instead traded him to the Phillies.
How'd Carlton respond to that deal? The next season, he went 27-10 with a 1.97 ERA in 346.1 innings of work while winning the Cy Young and finishing 5th in MVP voting.
Carlton went on to win three more Cy Youngs after that, finish top-4 two more times, top 15 in MVP voting five more times, and become an All-Star six other times as well. All in all, Carlton went 241-161 with a 3.09 ERA in 3697.1 innings of work for the Phillies during his 15 years there.
Letting money get in the way of paying a Hall of Fame-level pitcher about to begin his prime is about as ridiculous as penny-pinching can get. Carlton is one of the best pitchers of all time and should be known as that in a Cardinal uniform. Instead, they dealt him for practically nothing and watched him shut down opponents for another 20 seasons.