Amazon.com: Timetec 16GB KIT(2x8GB) Compatible for Apple DDR3 1333MHz PC3-10600 CL9 for Mac Book Pro (Early/Late 2011 13/15/17 inch), iMac(Mid 2010, Mid/Late 2011 21.5/27 inch), Mac Mini(Mid 2011) MAC RAM Upgrade :
iMac RAM for Model 11.2 to 12.2 | DDR3-1066MHz | 4GBx4 | MacMemory.com
Is it worth it to upgrade RAM on Mid 2010 21.5 iMac? | MacRumors Forums
Apple iMac 2010 (Mid) 21.5-inch (iMac 11,2) SSD ,Ram & OSX Upgrades - ZD Laptop Service Centre
NEMIX RAM 32GB (4x8GB Upgrade) DDR3-1333 PC3-10600 204-Pin SODIMM Memory for Apple MacBook Pro Early/Late 2011, iMac Mid 2010 27 inch 4-Core, iMac Mid 2011 21.5/27” , Mac Mini Mid 2011 at Amazon.com
16GB 2X 8GB DDR3 RAM MEMORY FOR APPLE IMAC MODEL# IMAC11,2 IMAC11,3 A1311 A1312 | eBay
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
How to Upgrade iMac RAM (21.5" and 27" Aluminum): EveryMac.com
Install memory in an iMac - Apple Support
8GB [2x4GB] DDR3-1333 RAM Memory Upgrade Kit for The Apple iMac 11,2 (21.5-inch, 3.2GHz, MC509LL/A) Intel Core i3 (Genuine A-Tech Brand) at Amazon.com
Best Buy: Apple® iMac® / Intel® Core™ i3 Processor / 27" Display / 4GB Memory / 1TB Hard Drive MC510LL/A