CMS 16GB (4X4GB) DDR3 10600 1333MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core I3 3.06 21.5-Inch (Mid-2010) - A28 at Amazon.com
A-Tech 32GB (4x8GB) RAM for Apple iMac (Mid 2010 27 inch 4-Core, Mid 2011 21.5/27 inch) | DDR3 1333MHz PC3-10600 204-Pin SODIMM Memory Upgrade Kit at Amazon.com
Amazon.com: Timetec 32GB KIT(4x8GB) Compatible for Apple DDR3 1333MHz PC3-10600 CL9 for iMac (Mid 2010 27 inch, Mid 2011 21.5/27 inch) SODIMM Memory Module MAC RAM Upgrade for iMac 11,3 / iMac 12,1 / iMac 12, 2 : Electronics
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
Install memory in an iMac - Apple Support
iMac 27" 3.4GHz (Late 2013) | mac of all trades
Memory Upgrades for iMac 27-Inch (2012 - Mid 2015)
CMS 16GB (4X4GB) DDR3 10600 1333MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core I3 3.06 21.5-Inch (Mid-2010) - A28 at Amazon.com
32.0GB OWC Memory Upgrade Kit For 2010-2011 Apple iMac
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
Install memory in an iMac - Apple Support
iMac RAM for Model 11.2 to 11.3 (i3) | Mid 2010 | RAMJET.com
Is it worth it to upgrade RAM on Mid 2010 21.5 iMac? | MacRumors Forums