The Germen acquisition by the Yankees was the first deal between the two teams in 10 years. Before the 2005 season, the Yankees re-acquired LHP Mike Stanton from the Mets in exchange for LHP Felix Heredia. Prior to that, the Mets dealt reliever Armando Benitez in July of 2003 to the Yankees for pitchers Anderson Garcia and Jason Anderson as well as a minor leaguer. At the time of this deal, it was about a year and a half since the Mets traded 3B Robin Ventura to the Yankees for OF David Justice in the 2001 off season. Justice was then dealt by the Mets to the Oakland Athletics for LHP Mark Guthrie and RHP Tyler Yates.
Prior to the 2001 off season, it had been over 8 years since the two teams made a deal with each other. That was when, in September of 1993, the Mets dealt veteran LHP Frank Tanana to the Yankees in exchange for RHP Kenny Greer. Tanana, the 21 year veteran who won 240 games for his career, pitched in three games down the stretch for the Yankees. Those three games were the last of Tanana's career. Greer pitched in one game for the the Mets in 1993, then 8 more the San Francisco Giants in 1995.
Not counting the players who were purchased by either club from each other, the Yankees and Mets have made a total of ten trades in the past 53 years. The first one, oddly enough did not involve either team trading a player to each other. The Mets, Yankees and Expos agreed on a three way deal that sent 1B Dave McDonald from the Expos to the Mets and a minor leaguer from the Yankees to the Expos. The first deal between the two teams that was not a cash deal happened on December 9, 1977 and saw the Yankees sending infielder Sergio Ferrer to the Mets in exchange for 1B Roy Staiger. Prior to the start of the 1983 season, the Yankees dealt OF Tucker Ashford and a minor leaguer to the Mets for a minor leaguer.
After the 1987 season, the Mets and Yankees made their biggest deal to date when the Yankees acquired World Series Champion SS Rafael Santana from the Mets for LHP Steve Frey, OF Darren Reed and C Phil Lombardi. Lombardi and Reed would play for the Mets and Frey would be traded to the Expos before he made it to the major leagues. In the middle of the 1989 season, the Mets dealt OF Marcus Lawton to the Yankees for RHP Scott Nielsen, neither of whom helped the other at the major league level. Finally, in June of 1992, the Mets dealt RHP Tim Burke to the Yankees for LHP Lee Guetterman.
In case you were interested in who else was purchased by either club, the Mets in 1967 purchased Bob Friend (a guest on the Passed Ball Show) from the Yankees and in 1967 purchased RHP Hal Reniff. Prior to the 1980 season, the Yankees purchased 1B Marshall Brant from the Mets, making his MLB debut for the Yankees that season. I find a lot of intrigue in the trade history of clubs, so I will continue over the next couple of weeks profiling a certain city and its history of trades between two (or more) teams.