How to Upgrade Memory in a 21.5-inch or 27-inch iMac (Mid 2010) - YouTube
OWC 8 GB (2 X 4GB) ram PC8500 DDR3 1066MHz sodimm 204-pin Memory Upgrade Kit, (OWC8566DDR3S8GP), Compatible with MacBook Pro, MacBook, Mac Mini and iMac at Amazon.com
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
Installing additional SSD in Mid-2010 27" iMac
Apple iMac 21.5-Inch Core i3 3.2 Mid 2010 4GB RAM High Sierra 500GB HD Disk CD | eBay
2GB DDR3 1333 SODIMM for Apple iMac (Mid 2010,2011, Late 2011), Mac Mi – Aplus Technology
Timetec Hynix IC 16GB KIT(2x8GB) Compatible for Apple DDR3 PC3-8500 1067MHz/1066MHz Upgrade for MacBook 13'' Mid 2010, MacBook Pro 13'' Mid 2010, iMac 27''Late 2009, Mac Mini Mid 2010(16GB KIT(2x8GB)) Laptop Memory -