OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
OFFTEK 4GB Replacement Memory RAM Upgrade for Apple iMac 2.66GHz Intel Core 2 Duo - (24-Inch) (DDR3) (MB418LL/A - Early 2009) (DDR3-8500) Desktop Memory at Amazon.com
Don't Upgrade The RAM In Your New Apple iMac, Do This Instead
How to Upgrade the iMac 24-inch (Early 2009)
iMac | 2.66 GHz Core 2 Duo | 24 Inch | Early 2009 - Techable.com