A-Tech 16GB (4x4GB) RAM for Apple iMac (Mid 2010, Mid 2011, Late 2011) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
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
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
iMac 20" Mid 2007 🔥WITH T9500 CPU UPGRADE🔥 MAX 6GB RAM, 480GB SSD 10.11 OSX | eBay
Apple 21.5-inch iMac review | 2014 | Digital Trends
iMac Pro: Discontinued! Don't Buy an iMac Pro
Third-Party RAM for 27-inch iMac Still Far More Affordable Than Apple's Checkout Upgrade Options - MacRumors