As I sit here trying to think of what might have been the best baseball trade ever, value for value, benefiting both teams involved, the one I keep coming back to is in 1990 when the Toronto Blue Jays sent Fred McGriff and Tony Fernandez to the San Diego Padres for Joe Carter and Roberto Alomar. 4 all-stars changed teams in this deal. One Hall of Famer (Alomar) and one guy who arguably should be in the Hall of Fame (McGriff). Joe Carter would go on to hit the most important homerun in Blue Jay history. Value for value, I don't think either team could argue about the production they received from the players they acquired.
Is there any other trade in the history of the game that comes close to being as big a deal for the teams involved than this one?