A-Tech 16GB (2x8GB) RAM for Apple MacBook Pro (Early/Late 2011), iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch), Mac Mini (Mid 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
4GB G.Skill DDR3 PC3-12800 1600MHz CL11 NT Series Desktop Memory Module
Kingston PC3-12800 4 GB 1600 MHz DDR3 SDRAM Memory (KVR16N11S8/4) for sale online | eBay