Recommended Spark-Plugs Subaru

STi 2.5 (2004-2006)
NGK ILFR6B. LFR6A-11 or LFR6AIX-11 if you want iridium.
Denso Iridium IKH22 one step colder  
NGK iridium LFR7AIX one step colder 
NGK iridium ILFR7H

WRX 2.0 (2002-2005):
NGK/Copper/BKR6ES/WRX/stock
NGK/Copper/BKR7ES/WRX/one step colder
NGK/Copper/BKR6E/WRX/stock
NGK/Copper/BKR7E/WRX/one step colder
NGK/Platinum/BKR6EGP/WRX/stock
NGK/Platinum/BKR7EGP/WRX/one step colder
NGK/Platinum/PFR6G/WRX/stock <----OEM plug
NGK/Platinum/PFR7G/WRX/one step colder
NGK/Iridium/BKR6EIX/WRX/stock
NGK/Iridium/BKR7EIX/WRX/one step colder
Denso/Iridium/IK20/WRX/stock
Denso/Iridium/IK22/WRX/one step colder