Ramjet now carries DDR3-1333 RAM upgrades for the latest rev of the iMac line. The new iMacs have four memory slots, and a system maximum of 16GB.  

Ramjet offers a 4Gig kit (2x 2Gig modules), an 8GB Kit (2x 4GB modules), and a 16GB kit (4x 4GB modules). These modules are fully compatible with the latest Apple firmware, and are SPD configured for the new iMac. These kits are shipping now, and are covered by a lifetime warranty. For details go to http://www.ramjet.com/imi.asp#1333 .