4GB (1x4GB) DDR3-1333MHz PC3-10600 2Rx8 SODIMM Laptop Memory by NEMIX RAM at Amazon.com
Timetec Hynix IC 4GB Compatible for Apple DDR3 1333MHz PC3-10600 SODIMM Memory for Early/Late 2011 13/15/17 inch MacBook Pro, Mid 2010 and Mid/ Late 2011 21.5/27 inch iMac, Mid 2011 Mac Mini (4GB) - Newegg.com