4GB DDR3-1600MHz PC3-12800 240-pin 1.5V 1Rx8 Non-ECC Unbuffered Desktop Memory by NEMIX RAM at Amazon.com
G.Skill Ripjaws X Series 16 GB (2 x 8 GB) 240-Pin SDRAM (PC3-12800) DDR3 1600 CL10-10-10-30 1.50V Dual Channel Desktop Memory Model F3-12800CL10D-16GBXL 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
Synology RAM DDR4-2666 Non-ECC SO-DIMM 4GB (D4NESO-2666-4G) at Amazon.com
Samsung 4GB DDR3 PC3-12800 1600MHz 204-Pin SODIMM Laptop Memory Module RAM. Model M471B5273DH0-CK0 at Amazon.com