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
How to Upgrade iMac RAM (20" and 24" Aluminum): EveryMac.com
Timetec Hynix IC DDR3L 1600MHz PC3L-12800 SODIMM Compatible with Apple 2011, 2012, 2013, 2014 MacBook Pro, iMac, Mac mini (16GB Kit(2x8GB)) - Newegg.com
Memory Upgrades for Apple iMac 2008 - Up to 6GB
Install memory in an iMac - Apple Support
4GB Kit (2GBX2) DDR2 800MHz RAM Memory Upgrade for Apple iMac Core 2 Duo 20-inch (Early 2008) (PARTS-QUICK) - Walmart.com
NEW 8 GB RAM upgrade for MacBook Pro (2008-2012), iMac, Mini. Lifetime Warranty | eBay
4GB Kit Apple iMac (April 2008) Memory Upgrade 2 x 2GB (MB413G/A) DDR2 PC2-6400 SODIMMs at Amazon.com
Maximum RAM iMac early 2008 | MacRumors Forums
Memory Upgrades for Apple iMac 2011 Up to 32GB
Install memory in an iMac - Apple Support
CMS 6GB (1X4GB) & (1X2GB) DDR2 6400 800MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac Core 2 Duo 2.4 20-Inch Early 2008 - B117 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