OWC 16.0GB (4 x 4GB) 1333MHz 204-Pin DDR3 SO-DIMM PC3-10600 CL9 Memory Compatible with iMac (OWC1333DDR3S16S) at Amazon.com
Install memory in an iMac - Apple Support
How To Upgrade the RAM on the New 27-Inch iMac (2020) & Save Money! $$ - YouTube
Timetec 8GB Compatible for Apple Late 2015 iMac (27-inch w/Retina 5K Display) DDR3L 1867MHz / 1866MHz PC3L-14900 2Rx8 CL13 1.35V 204 Pin SODIMM Memory Module MAC RAM Upgrade for iMac 17,1 at Amazon.com
Memory Upgrades for iMac 21.5-Inch 2019
OWC 32GB (2 x 16GB) PC21300 DDR4 2666MHz SO-DIMMs Memory, Compatible with Mac Mini 2018, iMac 2019 and up, and Compatible PCs, (OWC2666DDR4S32P) at Amazon.com
How to upgrade the 27-inch 5K iMac (2019) with a massive 128GB of RAM [Video] - 9to5Mac
CMS 4GB (2X2GB) DDR2 5300 667MHZ NON ECC SODIMM Memory Ram Upgrade Compatible with Apple® Imac (Mid 2007) Pc2-5300 - A37 System Specific Memory - Newegg.com
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
How to Upgrade iMac RAM: 2012-2022: EveryMac.com
Amazon.com: Timetec 16GB KIT(2x8GB) Compatible for Apple DDR3L 1600MHz for Mac Book Pro(Early/Late 2011,Mid 2012), iMac(Mid 2011,Late 2012,Early/Late 2013,Late 2014,Mid 2015), Mac Mini(Mid 2011,Late 2012) MAC RAM : Electronics
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
NEMIX RAM Compatible for 128GB (4x32GB) DDR4 2666MHz PC4-21300 SODIMM Memory Upgrade for Apple iMac Mid 2020 (iMac 20,1/20,2) / Mid 2019 (iMac19,1) 27-inch w/Retina 5K, Late 2018 Mac Mini 8,1 at Amazon.com