This is another one where the Astros got a gift in acquiring the player in the first place and punted the opportunity away. Curt Schilling started his career with the Red Sox before getting traded to the Orioles in 1988. He would eventually get shifted to the bullpen in Baltimore before Houston swiped him in a trade in 1991.
Unfortunately, that is where the good news for Houston ended. The Astros were really wheeling and dealing back in those days to manage their payroll. After Schilling posted a 3.81 ERA out of the bullpen for Houston in 56 appearances in 1991, the Astros would trade him to the Phillies at the beginning of the 1992 season.
The rest, of course, is history. Schilling would go on to be one of the league's most steady starters in Philly before going on to the Diamondbacks and Red Sox to cement his legacy as one of the best pitchers of his era.
If you look at the top of most "worst Astros trades of all-time" lists, you are likely to find Joe Morgan's name. Morgan spent the first nine seasons of his career with Astros where he compiled a .263/.375/.396 line in almost 4,000 plate appearances. After being in the league for THAT long, you would think that Morgan was what his numbers said he was.
Looking to upgrade their offense and dealing with the fact that Astros manager Harry Walker was not a fan of Morgan, Houston dealt Morgan to the Reds after the 1971 season. As a part of the Big Red Machine, Morgan would break out in a huge way with a .288/.415/.470 line over eight seasons with 406 stolen bases and 152 homers and getting inducted into the Hall of Fame in 1990 the first year he was eligible.
If you are looking for a silver lining here, it is that Morgan would return to the Astros in 1980 in the twilight of his career and spoke fondly of his time in Houston. Unfortunately, the team just didn't get the benefit of the prime of his career.