CMS 4GB (1X4GB) DDR2 6400 800MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core 2 Duo 2.4 20-Inch Early 2008 - A42 at Amazon.com
Timetec Hynix IC 4GB Compatible for Apple DDR3L 1600MHz PC3L-12800 SODIMM Memory Upgrade for Early/Mid/Late 2011, Mid/Late 2012, Early/Late 2013, Late 2014, Mid 2015 MacBook Pro, iMac, Mac Mini (4GB) - Walmart.com
4GB Kit Apple iMac (April 2008) Memory Upgrade 2 x 2GB (MB413G/A) DDR2 PC2-6400 SODIMMs at Amazon.com
iMac (2007-2009) Memory Installation Video - YouTube
How to Upgrade the RAM in Your iMac
iMac Memory for Model 8.1 | DDR2-800MHz |4GB | MacMemory.com