A-Tech 8GB 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 Module at Amazon.com
Apple iMac 27" 5K All-In-One Computer, Intel Core i5, 8GB RAM, 1TB HD & 128GB SSD, Mac OS, Silver, MF886LL/A (Certified Used) - Walmart.com
iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET