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 at Amazon.com
4GB Memory for Apple iMac Late 2015 27-inch 1867MHz DDR3 SO-DIMM (PARTS-QUICK Brand) at Amazon.com
CMS 4GB (1X4GB) DDR2 6400 800MHZ NON ECC SODIMM Memory Ram Upgrade Compatible with Apple® Imac 24-Inch 2.8Ghz Intel Core 2 Duo (MB325Ll/A - A42 - Walmart.com
Crucial 8GB Kit (2 x 4GB) DDR3L-1333 SODIMM Memory for Mac | CT2K4G3S1339M | Crucial.com
Crucial 4GB DDR3L-1333 SODIMM Memory for Mac | CT4G3S1339M | Crucial.com
Amazon.com: OWC 8GB (2 x 4GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S08P) : Everything Else
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
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