4GB -2x2GB Memory Ram Upgrade 20" Apple iMac-8.1 2.4GHz Core 2 Duo Early 2008 | eBay
How to Upgrade iMac RAM (20" and 24" Aluminum): EveryMac.com
Apple iMac A1225 24" Desktop - MB325LL/A (April, 2008) for sale online | eBay
Apple iMac 20-inch 2.0GHz Core 2 Duo 2GB Ram 160GB Hard Drive - MC015LL/A (Used) - Walmart.com
Install memory in an iMac - Apple Support
A-Tech for Apple 6GB Kit (1x2GB + 1x4GB) DDR2 667MHz PC2-5300 200-pin SODIMM for MacBook (Late 2007, Early 2008, Early 2009), MacBook Pro (Mid 2007, Early 2008), iMac (Mid 2007) - Memory RAM Upgrade at Amazon.com
Apple iMac (24-inch Penryn) - Review 2008 - PCMag UK