Apple iMac 2.5Ghz i5-2400S (Mid-2011) *No HDD/RAM* – MSU Surplus Store
Amazon.com: Timetec 16GB KIT(2x8GB) Compatible for Apple DDR3 1333MHz PC3-10600 CL9 for Mac Book Pro (Early/Late 2011 13/15/17 inch), iMac(Mid 2010, Mid/Late 2011 21.5/27 inch), Mac Mini(Mid 2011) MAC RAM Upgrade :
iMac: How to remove or install memory
Apple shows you how to upgrade your new iMac's RAM - 9to5Mac