Micron 4GB PC3-10600 DDR3-1333MHz (MT18JSF51272AZ-1G4D1) at Amazon.com
A-Tech 4GB RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010, Mid 2011, Late 2011), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Module at Amazon.com
Patriot PVS34G1333LLK Extreme Performance Viper Series PC3-10666 DDR3 1333MHz 4GB CAS 7-7-7-20 Low Latency Dual Channel Kit (Silver) at Amazon.com