According to SBNation's Chris Cotillo, the following Mets have elected free agency as per Article XX-D.
RHP John Lannan
C Taylor Teagarden
SS Omar Quintanilla
Article XX-D allows players with more than 3 years of service time and either A) less than 5 years of service time or B) have been previously outrighted off a 40 man roster, become free agents immediately after the end of the MLB regular season (post Wild Card play-in games).