iMac (2007-2009) Memory Installation Video - YouTube
How to Upgrade iMac RAM (20" and 24" Aluminum): EveryMac.com
8GB (4GBx2) Team High Performance Memory RAM Upgrade for iMac “Core 2 Duo” 2.66 20-Inch (Early 2008) MB324LL/A iMac 8,1. The Memory Kit Comes with Life Time Warranty. at Amazon.com
CMS 2GB (1X2GB) RAM Memory 4 Apple iMac "Core 2 Duo" 2.4 20-Inch Early 2008 - Walmart.com
4GB Kit Apple iMac (April 2008) Memory Upgrade 2 x 2GB (MB413G/A) DDR2 PC2-6400 SODIMMs at Amazon.com
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
Maximum RAM iMac early 2008 | MacRumors Forums
parts-quick 6GB Kit (4GB + 2GB) Memory for iMac 2008 Apple MacBook 2009 PC2-6400 800MHz DDR2 SODIMM at Amazon.com
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
Install memory in an iMac - Apple Support
Good Condition Apple iMac Early 2008, 250GB Storage, 5GB RAM, 2.4GHz | eBay
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