CMS 4GB (2X2GB) DDR2 5300 667MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Apple® iMac (Mid 2007) Pc2-5300 - A37 at Amazon.com
Install memory in an iMac - Apple Support
Memory Upgrades for Apple iMac 2007 - Up to 6GB
Install memory in an iMac - Apple Support
Apple iMac 20-inch Mid 2007 Core 2 Duo Processor 2.4 GHz 250GB HDD 3GB RAM | eBay
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
Install memory in an iMac - Apple Support
How to replace HDD/SSD in iMac Mid 2007/Early 2008/Early 2009/Mid 2009 | Mac Cheat Sheet
The infamous 2007 iMac on Catalina | MacRumors Forums