8GB -2x4GB Memory Ram Upgrade for 27" Apple iMac-12.2 Core i5 3.1GHz Mid 2011 | eBay
New 16GB 4x4GB Memory Apple iMac (21.5 and 27-inch, Mid 2011) PC3-10600 at Amazon.com
How to upgrade RAM on iMac 21.5" 2011 - YouTube
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
Memory Upgrades for Apple iMac 2011 Up to 32GB
CMS 32GB (4X8GB) DDR3 10600 1333MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core I7 3.4 27-Inch (Mid-2011) - C12 at Amazon.com
Upgrade Options for Apple iMac 27-Inch 2011
HOW TO: Upgrade The RAM to 32GB on a Mid-2011 21.5inch iMac - YouTube
OFFTEK 2GB Replacement Memory RAM Upgrade for Apple iMac 2.5GHz Intel Quad-Core i5 - (21.5-Inch) (DDR3 - Mid 2011) (DDR3-10600) Desktop Memory at Amazon.com
21.5 inch late 2013 iMac - RAM upgrade - Apple Community