Memory RAM Upgrade for Apple iMac 21.5-inch Mid 2011 4GB/8GB DDR3 SODIMM | eBay
I recently purchased 2011 21.5 iMac (Mid-2011) and I'm obsessed. : r/mac
Timetec Hynix IC 4GB Compatible for Apple DDR3 1333MHz PC3-10600 SODIMM Memory for Early/Late 2011 13/15/17 inch MacBook Pro, Mid 2010 and Mid/ Late 2011 21.5/27 inch iMac, Mid 2011 Mac Mini (4GB) - Newegg.com
Apple iMac compatible RAM and SSD upgrades | Upgradeable
Timetec Hynix IC 8GB KIT(2x4GB) Compatible for Apple DDR3 1333MHz PC3-10600 for Early/Late 2011 13/15/17 inch MacBook Pro, Mid 2010 Mid/Late 2011 21.5/27 inch iMac, Mid 2011 Mac Mini (8GB KIT(2x4GB)) - Walmart.com
How To Upgrade RAM in a Mac | Macworld
Buy Timetec 8GB KIT(2x4GB) Compatible for Apple DDR3 1333MHz PC3-10600 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) RAM Upgrade Online at