Cespedes was a runner-up in A.L. Rookie of the Year voting for 2012, making his first All-Star appearance this season. He brings the Red Sox a 3-season average of 22 HR's, 24 Doubles, and an OPS of .788 according to current statistics on Baseball-Reference. He currently leads the league in Assists as an OF.
In return, the Athletics aquired Jon Lester and Jonny Gomes. Lester is a 3-time All-Star that's averaged over 200 innings per season since he began pitching regularly during his third season as a Boston Starter in 2008.
Lester also brings 4 years of postseason experience, including 2 World Series championships with an overall 2.11 ERA in 76.2 postseason innings pitched.
...Gomes is a former Athletics player that's originally from California. He brings 3 years of postseason experience to an Oakland ballclub that is primed for a 2014 postseason appearance as a team with the current best record in baseball.
Gomes currently has a career OPS of .781.