Memory RAM Upgrade for Apple iMac 21.5-inch Mid 2011 4GB/8GB DDR3 SODIMM | eBay
iMac RAM for Model 11.2 to 12.2 | DDR3-1066MHz | 8GBx2 | MacMemory.com
Apple iMac 2011 32GB 4x8GB DDR3 1333MHz PC3-10600 204-Pin
Apple iMac 2011 Memory 4GB DDR3 1333MHz PC3-10600 204-Pin
Install memory in an iMac - Apple Support
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
iMac 21.5" Mid 2011 How To Change/Upgrade Your Ram For Better Performance 2014 - YouTube
32GB (4 x 8GB) PC10600 DDR3 1333MHz SO-DIMMs Memory Compatible with 2011 MacBook Pro, Mid 2010/2011 21.5" & 27" iMac Models, 2011 Mac Mini (OWC1333DDR3S32S) at Amazon.com
16GB [4x4GB] DDR3 RAM Memory for Apple iMac 2011 21.5" Intel Core i5 2.5 2.7 GHz | eBay
Amazon.com: Timetec 32GB KIT(4x8GB) Compatible for Apple DDR3 1333MHz PC3-10600 CL9 for iMac (Mid 2010 27 inch, Mid 2011 21.5/27 inch) SODIMM Memory Module MAC RAM Upgrade for iMac 11,3 / iMac 12,1 / iMac 12, 2 : Electronics
Adamanta 16GB (2x8GB) Apple Memory Upgrade DDR3L 1600MHz SODIMM Compatible for iMac (Mid 2011, Late 2012, Early/Late 2013, Late 2014, Mid 2015), MacBook Pro (Early/Late 2011, Mid 2012), Mac Mini at Amazon.com